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|
<HTML
><HEAD
><TITLE
>The xine hacker's guide</TITLE
><META
NAME="GENERATOR"
CONTENT="Modular DocBook HTML Stylesheet Version 1.7"></HEAD
><BODY
CLASS="BOOK"
><DIV
CLASS="BOOK"
><A
NAME="AEN1"
></A
><DIV
CLASS="TITLEPAGE"
><H1
CLASS="TITLE"
><A
NAME="AEN2"
></A
>The xine hacker's guide</H1
><H3
CLASS="AUTHOR"
><A
NAME="AEN6"
></A
>Günter Bartsch</H3
><H3
CLASS="AUTHOR"
><A
NAME="AEN9"
></A
>Heiko Schäfer</H3
><H3
CLASS="AUTHOR"
><A
NAME="AEN12"
></A
>Richard Wareham</H3
><H3
CLASS="AUTHOR"
><A
NAME="AEN15"
></A
>Miguel Freitas</H3
><H3
CLASS="AUTHOR"
><A
NAME="AEN18"
></A
>James Courtier-Dutton</H3
><H3
CLASS="AUTHOR"
><A
NAME="AEN21"
></A
>Siggi Langauf</H3
><H3
CLASS="AUTHOR"
><A
NAME="AEN24"
></A
>Marco Zühlke</H3
><H3
CLASS="AUTHOR"
><A
NAME="AEN27"
></A
>Mike Melanson</H3
><H3
CLASS="AUTHOR"
><A
NAME="AEN30"
></A
>Michael Roitzsch</H3
><P
CLASS="COPYRIGHT"
>Copyright © 2001-2003 the xine project team</P
><DIV
><DIV
CLASS="ABSTRACT"
><A
NAME="AEN36"
></A
><P
></P
><P
> This document should help xine hackers to find their way through
xine's architecture and source code. It's a pretty free-form document
containing a loose collection of articles describing various aspects
of xine's internals.
</P
><P
></P
></DIV
></DIV
><HR></DIV
><DIV
CLASS="TOC"
><DL
><DT
><B
>Table of Contents</B
></DT
><DT
>1. <A
HREF="#INTRO"
>Introduction</A
></DT
><DD
><DL
><DT
><A
HREF="#AEN40"
>Where am I?</A
></DT
><DT
><A
HREF="#AEN44"
>What does this text do?</A
></DT
><DT
><A
HREF="#AEN47"
>New versions of this document</A
></DT
><DT
><A
HREF="#AEN54"
>Feedback</A
></DT
></DL
></DD
><DT
>2. <A
HREF="#XINE-LIBRARY"
>Using the xine library</A
></DT
><DD
><DL
><DT
><A
HREF="#AEN61"
>xine architecture as visible to libxine clients</A
></DT
><DT
><A
HREF="#AEN75"
>Writing a new frontend to xine</A
></DT
><DD
><DL
><DT
><A
HREF="#AEN78"
>Source code of a simple X11 frontend</A
></DT
></DL
></DD
></DL
></DD
><DT
>3. <A
HREF="#OVERVIEW"
>xine code overview</A
></DT
><DD
><DL
><DT
><A
HREF="#AEN83"
>Walking the source tree</A
></DT
><DT
><A
HREF="#AEN385"
>Object oriented programming in C</A
></DT
><DT
><A
HREF="#AEN396"
>Coding style and guidelines</A
></DT
><DT
><A
HREF="#AEN415"
>The xine logging system</A
></DT
><DD
><DL
><DT
><A
HREF="#AEN418"
>xine_log</A
></DT
><DT
><A
HREF="#AEN424"
>xprintf</A
></DT
><DT
><A
HREF="#AEN430"
>lprintf/llprintf</A
></DT
></DL
></DD
><DT
><A
HREF="#AEN443"
>How to contribute</A
></DT
></DL
></DD
><DT
>4. <A
HREF="#INTERNALS"
>xine internals</A
></DT
><DD
><DL
><DT
><A
HREF="#AEN448"
>Engine architecture and data flow</A
></DT
><DT
><A
HREF="#AEN461"
>Plugin system</A
></DT
><DD
><DL
><DT
><A
HREF="#AEN480"
>Plugin location and filesystem layout</A
></DT
><DT
><A
HREF="#AEN490"
>Plugin Content: What's inside the .so?</A
></DT
></DL
></DD
><DT
><A
HREF="#AEN529"
>What is this metronom thingy?</A
></DT
><DT
><A
HREF="#AEN542"
>How does xine synchronize audio and video?</A
></DT
><DT
><A
HREF="#OSD"
>Overlays and OSD</A
></DT
><DD
><DL
><DT
><A
HREF="#AEN571"
>Overlay Manager</A
></DT
><DT
><A
HREF="#AEN575"
>OSD Renderer</A
></DT
></DL
></DD
><DT
><A
HREF="#AEN610"
>MRLs</A
></DT
></DL
></DD
><DT
>5. <A
HREF="#STREAM"
>xine's stream layer</A
></DT
><DD
><DL
><DT
><A
HREF="#AEN620"
>Input layer</A
></DT
><DD
><DL
><DT
><A
HREF="#AEN632"
>Writing a xine input plugin</A
></DT
></DL
></DD
><DT
><A
HREF="#AEN676"
>Demuxer layer</A
></DT
><DD
><DL
><DT
><A
HREF="#AEN679"
>Introduction to demuxer theory</A
></DT
><DT
><A
HREF="#AEN683"
>Input considerations</A
></DT
><DT
><A
HREF="#AEN686"
>Seeking Policy</A
></DT
><DT
><A
HREF="#AEN693"
>Writing a xine demuxer</A
></DT
><DT
><A
HREF="#AEN733"
>Buffer types</A
></DT
></DL
></DD
><DT
><A
HREF="#AEN747"
>Decoder layer</A
></DT
><DD
><DL
><DT
><A
HREF="#AEN750"
>Audio and video decoders</A
></DT
><DT
><A
HREF="#AEN754"
>Video output formats</A
></DT
><DT
><A
HREF="#AEN757"
>Audio output formats</A
></DT
><DT
><A
HREF="#AEN760"
>Writing a xine decoder</A
></DT
><DT
><A
HREF="#AEN821"
>SPU decoder</A
></DT
></DL
></DD
></DL
></DD
><DT
>6. <A
HREF="#OUTPUT"
>xine's output layer</A
></DT
><DD
><DL
><DT
><A
HREF="#AEN836"
>Video output</A
></DT
><DD
><DL
><DT
><A
HREF="#AEN850"
>Writing a xine video out plugin</A
></DT
></DL
></DD
></DL
></DD
></DL
></DIV
><DIV
CLASS="CHAPTER"
><HR><H1
><A
NAME="INTRO"
></A
>Chapter 1. Introduction</H1
><DIV
CLASS="SECT1"
><H2
CLASS="SECT1"
><A
NAME="AEN40"
></A
>Where am I?</H2
><P
> You are currently looking at a piece of documentation for xine.
xine is a free video player. It lives on
<A
HREF="http://xinehq.de/"
TARGET="_top"
>http://xinehq.de/</A
>. Specifically
this document goes under the moniker of the "xine Hackers' Guide".
</P
></DIV
><DIV
CLASS="SECT1"
><HR><H2
CLASS="SECT1"
><A
NAME="AEN44"
></A
>What does this text do?</H2
><P
> This document should help xine hackers to find their way through
xine's architecture and source code. It's a pretty free-form document
containing a loose collection of articles describing various aspects
of xine's internals. It has been written by a number of people who work
on xine themselves and is intended to provide the important concepts and
methods used within xine. Readers should not consider this document to be
an exhausative description of the internals of xine. As with all projects
which provide access, the source-code should be considered the definitive
source of information.
</P
></DIV
><DIV
CLASS="SECT1"
><HR><H2
CLASS="SECT1"
><A
NAME="AEN47"
></A
>New versions of this document</H2
><P
> This document is being developed in the xine-lib cvs repository within
the directory <TT
CLASS="FILENAME"
>doc/hackersguide/</TT
>. If you are
unsure what to do with the stuff in that directory, please read the
<TT
CLASS="FILENAME"
>README</TT
> file located there.
</P
><P
> New versions of this document can also be obtained from the xine web site:
<A
HREF="http://xinehq.de/"
TARGET="_top"
>http://xinehq.de/</A
>.
</P
></DIV
><DIV
CLASS="SECT1"
><HR><H2
CLASS="SECT1"
><A
NAME="AEN54"
></A
>Feedback</H2
><P
> All comments, error reports, additional information and criticism
concerning this document should be directed to the xine documentations
mailing list <TT
CLASS="EMAIL"
><<A
HREF="mailto:xine-docs@lists.sourceforge.net"
>xine-docs@lists.sourceforge.net</A
>></TT
>.
Questions about xine hacking in general should be sent to the
developer mailing list <TT
CLASS="EMAIL"
><<A
HREF="mailto:xine-devel@lists.sourceforge.net"
>xine-devel@lists.sourceforge.net</A
>></TT
>.
</P
></DIV
></DIV
><DIV
CLASS="CHAPTER"
><HR><H1
><A
NAME="XINE-LIBRARY"
></A
>Chapter 2. Using the xine library</H1
><DIV
CLASS="SECT1"
><H2
CLASS="SECT1"
><A
NAME="AEN61"
></A
>xine architecture as visible to libxine clients</H2
><P
> The following drawing shows the components of xine as outside applications
see them. For every component, the functions for creating and destroying it
are given. Every other function works in the context it is enclosed in.
Functions that facilitate the connection of the individual components are
also given.
</P
><DIV
CLASS="MEDIAOBJECT"
><P
><IMG
SRC="library.png"><DIV
CLASS="CAPTION"
><P
>outside view on xine components</P
></DIV
></P
></DIV
><P
> The function are named just to give you an overview of what is actually
there. It is all thoroughly documented in the plublic header
<TT
CLASS="FILENAME"
>xine.h</TT
>, which is the main and preferably the only xine
header, clients should include. (xine/xineutils.h and the XML parser might
make an exception.)
</P
><P
> Details on the OSD feature can be found in the <A
HREF="#OSD"
>OSD section</A
>.
</P
></DIV
><DIV
CLASS="SECT1"
><HR><H2
CLASS="SECT1"
><A
NAME="AEN75"
></A
>Writing a new frontend to xine</H2
><P
> The best way to explain this seems to be actual code. Below you
will find a very easy and hopefully self-explaining xine frontend
to give you a start.
</P
><DIV
CLASS="SECT2"
><HR><H3
CLASS="SECT2"
><A
NAME="AEN78"
></A
>Source code of a simple X11 frontend</H3
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>/*
** Copyright (C) 2003 Daniel Caujolle-Bert <segfault@club-internet.fr>
**
** This program is free software; you can redistribute it and/or modify
** it under the terms of the GNU General Public License as published by
** the Free Software Foundation; either version 2 of the License, or
** (at your option) any later version.
**
** This program is distributed in the hope that it will be useful,
** but WITHOUT ANY WARRANTY; without even the implied warranty of
** MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
** GNU General Public License for more details.
**
** You should have received a copy of the GNU General Public License
** along with this program; if not, write to the Free Software
** Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
**
*/
/*
* compile-command: "gcc -Wall -O2 `xine-config --cflags` `xine-config --libs` -lX11 -lm -o xinimin xinimin.c"
*/
#include <stdio.h>
#include <string.h>
#include <math.h>
#include <X11/X.h>
#include <X11/Xlib.h>
#include <X11/Xutil.h>
#include <X11/keysym.h>
#include <X11/Xatom.h>
#include <X11/Xutil.h>
#include <X11/extensions/XShm.h>
#include <xine.h>
#include <xine/xineutils.h>
#define MWM_HINTS_DECORATIONS (1L << 1)
#define PROP_MWM_HINTS_ELEMENTS 5
typedef struct {
uint32_t flags;
uint32_t functions;
uint32_t decorations;
int32_t input_mode;
uint32_t status;
} MWMHints;
static xine_t *xine;
static xine_stream_t *stream;
static xine_video_port_t *vo_port;
static xine_audio_port_t *ao_port;
static xine_event_queue_t *event_queue;
static Display *display;
static int screen;
static Window window[2];
static int xpos, ypos, width, height, fullscreen;
static double pixel_aspect;
static int running = 0;
/* this will be called by xine, if it wants to know the target size of a frame */
static void dest_size_cb(void *data, int video_width, int video_height, double video_pixel_aspect,
int *dest_width, int *dest_height, double *dest_pixel_aspect) {
if(!running)
return;
*dest_width = width;
*dest_height = height;
*dest_pixel_aspect = pixel_aspect;
}
/* this will be called by xine when it's about to draw the frame */
static void frame_output_cb(void *data, int video_width, int video_height,
double video_pixel_aspect, int *dest_x, int *dest_y,
int *dest_width, int *dest_height,
double *dest_pixel_aspect, int *win_x, int *win_y) {
if(!running)
return;
*dest_x = 0;
*dest_y = 0;
*win_x = xpos;
*win_y = ypos;
*dest_width = width;
*dest_height = height;
*dest_pixel_aspect = pixel_aspect;
}
static void event_listener(void *user_data, const xine_event_t *event) {
switch(event->type) {
case XINE_EVENT_UI_PLAYBACK_FINISHED:
running = 0;
break;
case XINE_EVENT_PROGRESS:
{
xine_progress_data_t *pevent = (xine_progress_data_t *) event->data;
printf("%s [%d%%]\n", pevent->description, pevent->percent);
}
break;
/* you can handle a lot of other interesting events here */
}
}
int main(int argc, char **argv) {
char configfile[2048];
x11_visual_t vis;
double res_h, res_v;
char *vo_driver = "auto";
char *ao_driver = "auto";
char *mrl = NULL;
int i;
Atom XA_NO_BORDER;
MWMHints mwmhints;
/* parsing command line */
for (i = 1; i < argc; i++) {
if (strcmp(argv[i], "-vo") == 0) {
vo_driver = argv[++i];
}
else if (strcmp(argv[i], "-ao") == 0) {
ao_driver = argv[++i];
}
else
mrl = argv[i];
}
if (!mrl) {
printf("specify an mrl\n");
return 1;
}
printf("mrl: '%s'\n", mrl);
if (!XInitThreads()) {
printf("XInitThreads() failed\n");
return 1;
}
/* load xine config file and init xine */
xine = xine_new();
sprintf(configfile, "%s%s", xine_get_homedir(), "/.xine/config");
xine_config_load(xine, configfile);
xine_init(xine);
display = XOpenDisplay(NULL);
screen = XDefaultScreen(display);
xpos = 0;
ypos = 0;
width = 320;
height = 200;
/* some initalization for the X11 Window we will be showing video in */
XLockDisplay(display);
fullscreen = 0;
window[0] = XCreateSimpleWindow(display, XDefaultRootWindow(display),
xpos, ypos, width, height, 1, 0, 0);
window[1] = XCreateSimpleWindow(display, XDefaultRootWindow(display),
0, 0, (DisplayWidth(display, screen)),
(DisplayHeight(display, screen)), 0, 0, 0);
XSelectInput(display, window[0], (ExposureMask | ButtonPressMask | KeyPressMask |
ButtonMotionMask | StructureNotifyMask |
PropertyChangeMask | PointerMotionMask));
XSelectInput(display, window[1], (ExposureMask | ButtonPressMask | KeyPressMask |
ButtonMotionMask | StructureNotifyMask |
PropertyChangeMask | PointerMotionMask));
XA_NO_BORDER = XInternAtom(display, "_MOTIF_WM_HINTS", False);
mwmhints.flags = MWM_HINTS_DECORATIONS;
mwmhints.decorations = 0;
XChangeProperty(display, window[1],
XA_NO_BORDER, XA_NO_BORDER, 32, PropModeReplace, (unsigned char *) &mwmhints,
PROP_MWM_HINTS_ELEMENTS);
XMapRaised(display, window[fullscreen]);
res_h = (DisplayWidth(display, screen) * 1000 / DisplayWidthMM(display, screen));
res_v = (DisplayHeight(display, screen) * 1000 / DisplayHeightMM(display, screen));
XSync(display, False);
XUnlockDisplay(display);
/* filling in the xine visual struct */
vis.display = display;
vis.screen = screen;
vis.d = window[fullscreen];
vis.dest_size_cb = dest_size_cb;
vis.frame_output_cb = frame_output_cb;
vis.user_data = NULL;
pixel_aspect = res_v / res_h;
/* opening xine output ports */
vo_port = xine_open_video_driver(xine, vo_driver, XINE_VISUAL_TYPE_X11, (void *)&vis);
ao_port = xine_open_audio_driver(xine , ao_driver, NULL);
/* open a xine stream connected to these ports */
stream = xine_stream_new(xine, ao_port, vo_port);
/* hook our event handler into the streams events */
event_queue = xine_event_new_queue(stream);
xine_event_create_listener_thread(event_queue, event_listener, NULL);
/* make the video window visible to xine */
xine_port_send_gui_data(vo_port, XINE_GUI_SEND_DRAWABLE_CHANGED, (void *) window[fullscreen]);
xine_port_send_gui_data(vo_port, XINE_GUI_SEND_VIDEOWIN_VISIBLE, (void *) 1);
/* start playback */
if (!xine_open(stream, mrl) || !xine_play(stream, 0, 0)) {
printf("Unable to open mrl '%s'\n", mrl);
return 1;
}
running = 1;
while (running) {
XEvent xevent;
XNextEvent(display, &xevent);
switch(xevent.type) {
case KeyPress:
{
XKeyEvent kevent;
KeySym ksym;
char kbuf[256];
int len;
kevent = xevent.xkey;
XLockDisplay(display);
len = XLookupString(&kevent, kbuf, sizeof(kbuf), &ksym, NULL);
XUnlockDisplay(display);
switch (ksym) {
case XK_q:
case XK_Q:
/* user pressed q => quit */
running = 0;
break;
case XK_f:
case XK_F:
{
/* user pressed f => toggle fullscreen */
Window tmp_win;
XLockDisplay(display);
XUnmapWindow(display, window[fullscreen]);
fullscreen = !fullscreen;
XMapRaised(display, window[fullscreen]);
XSync(display, False);
XTranslateCoordinates(display, window[fullscreen],
DefaultRootWindow(display),
0, 0, &xpos, &ypos, &tmp_win);
XUnlockDisplay(display);
xine_port_send_gui_data(vo_port, XINE_GUI_SEND_DRAWABLE_CHANGED,
(void*) window[fullscreen]);
}
break;
case XK_Up:
/* cursor up => increase volume */
xine_set_param(stream, XINE_PARAM_AUDIO_VOLUME,
(xine_get_param(stream, XINE_PARAM_AUDIO_VOLUME) + 1));
break;
case XK_Down:
/* cursor down => decrease volume */
xine_set_param(stream, XINE_PARAM_AUDIO_VOLUME,
(xine_get_param(stream, XINE_PARAM_AUDIO_VOLUME) - 1));
break;
case XK_plus:
/* plus => next audio channel */
xine_set_param(stream, XINE_PARAM_AUDIO_CHANNEL_LOGICAL,
(xine_get_param(stream, XINE_PARAM_AUDIO_CHANNEL_LOGICAL) + 1));
break;
case XK_minus:
/* minus => previous audio channel */
xine_set_param(stream, XINE_PARAM_AUDIO_CHANNEL_LOGICAL,
(xine_get_param(stream, XINE_PARAM_AUDIO_CHANNEL_LOGICAL) - 1));
break;
case XK_space:
/* space => toggle pause mode */
if (xine_get_param(stream, XINE_PARAM_SPEED) != XINE_SPEED_PAUSE)
xine_set_param(stream, XINE_PARAM_SPEED, XINE_SPEED_PAUSE);
else
xine_set_param(stream, XINE_PARAM_SPEED, XINE_SPEED_NORMAL);
break;
}
}
break;
case Expose:
/* this handles (partial) occlusion of our video window */
if (xevent.xexpose.count != 0)
break;
xine_port_send_gui_data(vo_port, XINE_GUI_SEND_EXPOSE_EVENT, &xevent);
break;
case ConfigureNotify:
{
XConfigureEvent *cev = (XConfigureEvent *) &xevent;
Window tmp_win;
width = cev->width;
height = cev->height;
if ((cev->x == 0) && (cev->y == 0)) {
XLockDisplay(display);
XTranslateCoordinates(display, cev->window,
DefaultRootWindow(cev->display),
0, 0, &xpos, &ypos, &tmp_win);
XUnlockDisplay(display);
} else {
xpos = cev->x;
ypos = cev->y;
}
}
break;
}
}
/* cleanup */
xine_close(stream);
xine_event_dispose_queue(event_queue);
xine_dispose(stream);
xine_close_audio_driver(xine, ao_port);
xine_close_video_driver(xine, vo_port);
xine_exit(xine);
XLockDisplay(display);
XUnmapWindow(display, window[fullscreen]);
XDestroyWindow(display, window[0]);
XDestroyWindow(display, window[1]);
XUnlockDisplay(display);
XCloseDisplay (display);
return 0;
}</PRE
></TD
></TR
></TABLE
></DIV
></DIV
></DIV
><DIV
CLASS="CHAPTER"
><HR><H1
><A
NAME="OVERVIEW"
></A
>Chapter 3. xine code overview</H1
><DIV
CLASS="SECT1"
><H2
CLASS="SECT1"
><A
NAME="AEN83"
></A
>Walking the source tree</H2
><P
> The <TT
CLASS="FILENAME"
>src/</TT
> directory in xine-lib contains several
modules, this should give you a quick overview on where
to find what sources.
</P
><P
> Directories marked with "(imported)" contain
code that is copied from an external project into xine-lib.
Everything below such a directory is up to this project. When modifying
code there, be sure to send the patches on.
</P
><P
> <P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="FILENAME"
>audio_out</TT
></DT
><DD
><P
> Audio output plugins. These provide a thin abstraction layer
around different types of audio output architectures or platforms.
Basically an audio output plugin provides functions to query and setup
the audio hardware and output audio data (e.g. PCM samples).
</P
><P
></P
></DD
><DT
><TT
CLASS="FILENAME"
>demuxers</TT
></DT
><DD
><P
> Demuxer plugins that handle various system layer file formats
like avi, asf or mpeg. The ideal demuxer know nothing about where the
data comes from and who decodes it. It should basically just unpack
it into chunks the rest of the engine can eat.
</P
><P
></P
></DD
><DT
><TT
CLASS="FILENAME"
>dxr3</TT
></DT
><DD
><P
> Code to support the DXR3 / hollywood+ hardware mpeg decoder.
</P
><P
></P
></DD
><DT
><TT
CLASS="FILENAME"
>input</TT
></DT
><DD
><P
> Input plugins encapsulate the origin of the data. Data sources like
ordinary files, DVDs, CDA or streaming media are handled here.
</P
><P
> <P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="FILENAME"
>dvb</TT
></DT
><DD
><P
> Some headers for Digital Video Broadcast.
</P
><P
></P
></DD
><DT
><TT
CLASS="FILENAME"
>libdvdnav</TT
> (imported)</DT
><DD
><P
> The libdvdnav library for DVD navigation is used
by xine's DVD input plugin.
</P
><P
></P
></DD
><DT
><TT
CLASS="FILENAME"
>libreal</TT
>, <TT
CLASS="FILENAME"
>librtsp</TT
></DT
><DD
><P
> Support for RealMedia streaming as used by the RTSP input plugin.
</P
><P
></P
></DD
></DL
></DIV
>
</P
><P
></P
></DD
><DT
><TT
CLASS="FILENAME"
>liba52</TT
> (imported)</DT
><DD
><P
> A52 (aka AC3, aka Dolby Digital) audio decoder library and xine plugin.
</P
><P
> We maintain some small integration improving differences between the
original liba52 and our copy in the file
<TT
CLASS="FILENAME"
>diff_against_release.patch</TT
>.
</P
><P
></P
></DD
><DT
><TT
CLASS="FILENAME"
>libdivx4</TT
></DT
><DD
><P
> Video decoder plugin using libdivx4linux if it is installed.
Currently unmaintained and soon to be discontinued if noone cares to take over.
</P
><P
></P
></DD
><DT
><TT
CLASS="FILENAME"
>libdts</TT
></DT
><DD
><P
> Audio decoder plugin that does currently nothing but passing through
DTS (AC5) data to the audio output plugin. This is only usefull
when using an external hardware DTS decoder. James has started to
work on software DTS decoding, but has not succeeded so far. Anyone
giving him a hand?
</P
><P
></P
></DD
><DT
><TT
CLASS="FILENAME"
>libfaad</TT
> (imported)</DT
><DD
><P
> The Free AAC Decoder library and xine plugin.
</P
><P
></P
></DD
><DT
><TT
CLASS="FILENAME"
>libffmpeg</TT
></DT
><DD
><P
> A xine decoder plugin using various audio and video decoders from the
ffmpeg decoder pack libavcodec. Their MPEG encoder is also for the DXR3.
</P
><P
> To optimize the integration of libavcodec and the xine engine, we maintain
some differences between the original ffmpeg and our copy in the file
<TT
CLASS="FILENAME"
>diff_to_ffmpeg_cvs.txt</TT
>.
</P
><P
> <P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="FILENAME"
>libavcodec</TT
> (imported)</DT
><DD
><P
> The libavcodec decoder pack as used by xine's ffmpeg plugin.
</P
><P
></P
></DD
></DL
></DIV
>
</P
><P
></P
></DD
><DT
><TT
CLASS="FILENAME"
>libflac</TT
></DT
><DD
><P
> A xine demuxer and decoder plugin for the Free Lossless Audio Codec library,
which has to be installed separately.
</P
><P
></P
></DD
><DT
><TT
CLASS="FILENAME"
>liblpcm</TT
></DT
><DD
><P
> Audio decoder plugin that "decodes" raw PCM data; most notably
endianess-conversions are done here.
</P
><P
></P
></DD
><DT
><TT
CLASS="FILENAME"
>libmad</TT
> (imported)</DT
><DD
><P
> Mpeg audio decoder plugin (i.e. mp2 and mp3 decoding).
ISO/IEC compliant decoder using fixed point math.
</P
><P
></P
></DD
><DT
><TT
CLASS="FILENAME"
>libmpeg2</TT
> (imported)</DT
><DD
><P
> Most important MPEG video decoder plugin, provides fast and
high-precision MPEG-1/2 video decoding.
</P
><P
> Although this is an imported library, we have heavily modified
our internal copy to blend it as seamlessly as possible into
the xine engine in order to get the maximum MPEG decoding
performance.
</P
><P
></P
></DD
><DT
><TT
CLASS="FILENAME"
>libmpeg2new</TT
></DT
><DD
><P
> James started an effort to bring a recent and unmodified version
of libmpeg2 into xine to one day replace our current internal
modified libmpeg2 with one closer to the original. But since
the full feature catalog has not yet been achieved with the new
one, it is still disabled.
</P
><P
> <P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="FILENAME"
>include</TT
>, <TT
CLASS="FILENAME"
>libmpeg2</TT
> (imported)</DT
><DD
><P
> The code of the imported new libmpeg2.
</P
><P
></P
></DD
></DL
></DIV
>
</P
><P
></P
></DD
><DT
><TT
CLASS="FILENAME"
>libmpg123</TT
> (imported)</DT
><DD
><P
> An MPEG audio decoder plugin baseg on mpg123 code. This plugin is disabled
because it is unmaintained. Some people said, it was faster than the libmad
decoder. But if noone starts to fix it, it will disappear soon.
</P
><P
></P
></DD
><DT
><TT
CLASS="FILENAME"
>libreal</TT
></DT
><DD
><P
> A thin wrapper around Real's binary codecs from the Linux RealPlayer to
use them as a xine plugin.
</P
><P
></P
></DD
><DT
><TT
CLASS="FILENAME"
>libspeex</TT
></DT
><DD
><P
> A xine decoder plugin for the speex library,
which has to be installed separately.
</P
><P
></P
></DD
><DT
><TT
CLASS="FILENAME"
>libspucc</TT
></DT
><DD
><P
> Closed caption subtitle decoder plugin.
</P
><P
></P
></DD
><DT
><TT
CLASS="FILENAME"
>libspudec</TT
></DT
><DD
><P
> DVD SPU subtitle decoder plugin.
</P
><P
></P
></DD
><DT
><TT
CLASS="FILENAME"
>libsputext</TT
></DT
><DD
><P
> Plain text subtitle decoder plugins.
</P
><P
></P
></DD
><DT
><TT
CLASS="FILENAME"
>libtheora</TT
></DT
><DD
><P
> A xine decoder plugin for the theora library,
which has to be installed separately.
</P
><P
></P
></DD
><DT
><TT
CLASS="FILENAME"
>libvorbis</TT
></DT
><DD
><P
> A xine decoder plugin for the ogg/vorbis library,
which has to be installed separately.
</P
><P
></P
></DD
><DT
><TT
CLASS="FILENAME"
>libw32dll</TT
></DT
><DD
><P
> Video and audio decoder plugins that exploit some wine code
to use win32 (media player and Quicktime) codecs in xine.
Works on x86 platforms only.
</P
><P
> <P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="FILENAME"
>DirectShow</TT
>, <TT
CLASS="FILENAME"
>dmo</TT
>,
<TT
CLASS="FILENAME"
>qtx</TT
>, <TT
CLASS="FILENAME"
>wine</TT
> (imported)</DT
><DD
><P
> Stripped down version of wine to support Video for Windows DLLs
and additional code to use DirectShow, DMO and QuickTime DLLs.
</P
><P
></P
></DD
></DL
></DIV
>
</P
><P
></P
></DD
><DT
><TT
CLASS="FILENAME"
>libxineadec</TT
></DT
><DD
><P
> xine's decoder pack of additional audio decoders.
</P
><P
> <P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="FILENAME"
>gsm610</TT
> (imported)</DT
><DD
><P
> The gsm610 audio decoder library as used by the related xine plugin.
</P
><P
></P
></DD
><DT
><TT
CLASS="FILENAME"
>nosefart</TT
> (imported)</DT
><DD
><P
> The nosefart audio decoder library as used by the related xine plugin.
</P
><P
></P
></DD
></DL
></DIV
>
</P
><P
></P
></DD
><DT
><TT
CLASS="FILENAME"
>libxinevdec</TT
></DT
><DD
><P
> xine's decoder pack of additional video decoders.
</P
><P
></P
></DD
><DT
><TT
CLASS="FILENAME"
>libxvid</TT
></DT
><DD
><P
> A xine decoder plugin for the xvid library,
which has to be installed separately. This plugin is
unmaintained and unless someone cares to update it, it will
be moved to the attic soon.
</P
><P
></P
></DD
><DT
><TT
CLASS="FILENAME"
>post</TT
></DT
><DD
><P
> Video and audio post effect plugins live here. Post plugins
modify streams of video frames or audio buffers as they leave
the decoder to provide conversion or effects.
</P
><P
> <P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="FILENAME"
>deinterlace</TT
> (imported)</DT
><DD
><P
> The tvtime deinterlacer as a xine video filter post.
</P
><P
></P
></DD
><DT
><TT
CLASS="FILENAME"
>goom</TT
> (imported)</DT
><DD
><P
> The goom audio visualizer as a xine visualizer post.
</P
><P
></P
></DD
><DT
><TT
CLASS="FILENAME"
>mosaico</TT
></DT
><DD
><P
> Some post plugins merging multiple frames into one. For example
picture in picture can be done with this.
</P
><P
></P
></DD
><DT
><TT
CLASS="FILENAME"
>planar</TT
></DT
><DD
><P
> Some simple 2D video effects as xine video filter posts.
</P
><P
></P
></DD
><DT
><TT
CLASS="FILENAME"
>visualizations</TT
></DT
><DD
><P
> Audio visualization post plugins.
</P
><P
></P
></DD
></DL
></DIV
>
</P
><P
></P
></DD
><DT
><TT
CLASS="FILENAME"
>video_out</TT
></DT
><DD
><P
> Contains various video output driver plugins. Video output drivers
are thin abstraction layers over various video output platforms
(e.g. X11, directfb, directX,...). Video output driver plugins
provide functions like frame allocation and drawing and handle
stuff like hardware acceleration, scaling and colorspace conversion
if necessary. They do not handle a/v sync since this is done
in the xine-engine already.
</P
><P
> <P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="FILENAME"
>libdha</TT
> (imported)</DT
><DD
><P
> A library for direct hardware access to the graphics card
as used by the vidix video out plugin.
</P
><P
></P
></DD
><DT
><TT
CLASS="FILENAME"
>vidix</TT
> (imported)</DT
><DD
><P
> The vidix system for high performance video output
as used by the vidix video out plugin.
</P
><P
></P
></DD
></DL
></DIV
>
</P
><P
></P
></DD
><DT
><TT
CLASS="FILENAME"
>xine-engine</TT
></DT
><DD
><P
> The heart of xine - it's engine. Contains code to
load and handle all the plugins, the configuration repository
as well as the generic decoding loops and code for synchronized output.
A lot of helper functions for plugins to use live here as well.
What's in the individual files should be guessable by the files'
names. This document is not going to explain the source, because
it simply changes too often. A look at the architectural drawing
in the <A
HREF="#INTERNALS"
>internals section</A
> should
give you a pretty good idea, what to expect in this directory.
Basically, everything in this picture that is not called "plugin"
lives here.
</P
><P
></P
></DD
><DT
><TT
CLASS="FILENAME"
>xine-utils</TT
></DT
><DD
><P
> Collection of utility functions and platform abstractions.
Also contains a simple XML parser for frontend playlist handling.
</P
><P
></P
></DD
></DL
></DIV
>
</P
></DIV
><DIV
CLASS="SECT1"
><HR><H2
CLASS="SECT1"
><A
NAME="AEN385"
></A
>Object oriented programming in C</H2
><P
> xine uses a lot of design principles normally found in
object oriented designs. As xine is written in c, a few
basic principles shall be explained here on how xine
is object oriented anyway.
</P
><P
> Classes are structs containing function pointers and public member data.
Example:
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> typedef struct my_stack_s my_class_t;
struct my_stack_s {
/* method "push" with one parameter and no return value */
void (*push)(my_stack_t *this, int i);
/* method "add" with no parameters and no return value */
void (*add)(my_stack_t *this);
/* method "pop" with no parameters (except "this") and a return value */
int (*pop) (my_stack_t *this);
};
/* constructor */
my_class_t *new_my_stack(void);</PRE
></TD
></TR
></TABLE
>
</P
><P
> To derive from such a class, private member variables can be added:
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> typedef struct {
my_stack_t stack; /* public part */
/* private part follows here */
int values[MAX_STACK_SIZE];
int stack_size;
} intstack_t;</PRE
></TD
></TR
></TABLE
>
Each method is implemented as a static method (static to prevent
namespace pollution). The "this" pointer needs to be cast to the
private pointer type to gain access to the private member variables.
</P
><P
> Implementation of the "push" method follows:
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> static void push (my_stack_t *this_gen, int i) {
intstack_t *this = (intstack_t *)this_gen;
this->values[MAX_STACK_SIZE - ++this->stack_size] = i;
}</PRE
></TD
></TR
></TABLE
>
</P
><P
> Finally the contructor malloc()s the data struct (private variant)
and fills in function pointers and default values. Usually the
constructor is the only public (i.e. non-static) function in the module:
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> my_stack_t *new_my_stack(void) {
intstack_t *this;
/* alloc memory */
this = malloc(sizeof(intstack_t));
/* fill in methods */
this->push = push;
this->add = add;
this->pop = pop;
/* init data fields */
this->stack_size = 0;
/* return public part */
return &this->stack;
}</PRE
></TD
></TR
></TABLE
>
</P
></DIV
><DIV
CLASS="SECT1"
><HR><H2
CLASS="SECT1"
><A
NAME="AEN396"
></A
>Coding style and guidelines</H2
><P
> This section contains some guidelines for writing xine-code.
These are really just guidelines, no strict rules.
Contributions will not be rejected if they do not meet these
rules but they will be even more appreciated if they do.
<P
></P
><UL
><LI
><P
> Comment your interfaces directly in the header files.
No doxygen comments, ordinary C comments will do.
</P
></LI
><LI
><P
> Use C-style comments (/* */), not C++-style (//).
</P
></LI
><LI
><P
> When in doubt, use lower case. BTW: This thing is called xine, never Xine.
</P
></LI
><LI
><P
> Use expressive variable and function identifiers on all public interfaces.
Use underscores to seperate words in identifiers, not uppercase
letters (my_function_name is ok, myFunctionName is not ok).
</P
></LI
><LI
><P
> Avoid macros unless they are really useful. Avoid gotos.
</P
></LI
><LI
><P
> use something like
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> printf("module: ..."[,...]);</PRE
></TD
></TR
></TABLE
>
for console output. All console output goes to stdout and
must be prefixed by the module name which generates the
output (see example above).
</P
></LI
><LI
><P
> Refer to emac's C-mode for all questions of proper indentiation.
That first of all means: indent with two spaces.
</P
></LI
></UL
>
</P
></DIV
><DIV
CLASS="SECT1"
><HR><H2
CLASS="SECT1"
><A
NAME="AEN415"
></A
>The xine logging system</H2
><P
> xine offers a wide range of possibilities to display
strings. This section should describe when to use
which way and how to do it right.
</P
><DIV
CLASS="SECT2"
><HR><H3
CLASS="SECT2"
><A
NAME="AEN418"
></A
>xine_log</H3
><P
> Output which is done thru this function will be
displayed for the end user by the frontend.
If <TT
CLASS="VARNAME"
>xine->verbosity</TT
> is not 0 the messages will also
be displayed on the console. Ideally these strings
are translated.
This function is for information which the user should
read always.
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> xine_log(xine_t *xine, int buf, const char *format, ...);</PRE
></TD
></TR
></TABLE
>
<TT
CLASS="VARNAME"
>buf</TT
> is either XINE_LOG_MSG for general messages or
XINE_LOG_PLUGIN for messages about plugins.
</P
></DIV
><DIV
CLASS="SECT2"
><HR><H3
CLASS="SECT2"
><A
NAME="AEN424"
></A
>xprintf</H3
><P
> This macro uses the <TT
CLASS="VARNAME"
>xine->verbosity</TT
> value to decide
if the string should be printed to the console. Possible
values are XINE_VERBOSITY_NONE, XINE_VERBOSITY_LOG or
XINE_VERBOSITY_DEBUG. By default nothing is printed.
When you use xine-ui you can enable this output with
the <TT
CLASS="PARAMETER"
><I
>--verbose=[1,2]</I
></TT
> options.
This function should be used for information which the
user should only read up on request.
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> xprintf(xine_t *xine, int verbosity, const char *format, ...);</PRE
></TD
></TR
></TABLE
>
</P
></DIV
><DIV
CLASS="SECT2"
><HR><H3
CLASS="SECT2"
><A
NAME="AEN430"
></A
>lprintf/llprintf</H3
><P
> These macros are for debugging purpose only. Under normal
circumstances it is disabled. And can only be enabled by changing
a define statement and a recompilation. It has to be enabled for these
files that are of interest.
It should only be used for information which is intended for developers.
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> lprintf(const char *format, ...);
llprintf(bool, const char *format, ...);</PRE
></TD
></TR
></TABLE
>
<TT
CLASS="VARNAME"
>bool</TT
> is a flag which enables or disables this logging.
</P
><P
> <TT
CLASS="FUNCTION"
>lprintf</TT
> can be enabled by defining LOG at the top of the source file.
<TT
CLASS="FUNCTION"
>llprintf</TT
> can be used for more than one categorie
per file by using diffent lables:
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> #define LOG_LOAD 1
#define LOG_SAVE 0
llprintf(LOG_LOAD, "loading was successful\n");
llprintf(LOG_SAVE, "could not save to file %s\n", filename);</PRE
></TD
></TR
></TABLE
>
</P
><P
> In this case only the first messages is printed. To enable/disable change the defines.
</P
><P
> LOG_MODULE should be used to set the modulename for xprintf/lprintf/llprintf.
Each output line will start with "modulename: ".
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> #define LOG_MODULE "modulename"</PRE
></TD
></TR
></TABLE
>
</P
><P
> LOG_VERBOSE can be defined to enable the logging of functionname and linenumbers.
Then the output will be: "modulename: (function_name:42) message".
</P
></DIV
></DIV
><DIV
CLASS="SECT1"
><HR><H2
CLASS="SECT1"
><A
NAME="AEN443"
></A
>How to contribute</H2
><P
> Make sure you send your patches in unified diff format to
the xine-devel mailing list. You'll have to subscribe first,
otherwise you're not allowed to post. Please do not send
patches to individual developers unless instructed otherwise
because your patch is more likely to get lost in an overfull
INBOX in that case. Please be patient, it may take 1-2 weeks
before you hear any comments on your work (developers may be
working on other parts of the code or are simply busy at
the moment).
</P
></DIV
></DIV
><DIV
CLASS="CHAPTER"
><HR><H1
><A
NAME="INTERNALS"
></A
>Chapter 4. xine internals</H1
><DIV
CLASS="SECT1"
><H2
CLASS="SECT1"
><A
NAME="AEN448"
></A
>Engine architecture and data flow</H2
><DIV
CLASS="MEDIAOBJECT"
><P
><IMG
SRC="architecture.png"><DIV
CLASS="CAPTION"
><P
>xine engine architecture</P
></DIV
></P
></DIV
><P
> Media streams usually consist of audio and video data multiplexed
into one bitstream in the so-called system-layer (e.g. AVI, Quicktime or MPEG).
A demuxer plugin is used to parse the system layer and extract audio and video
packages. The demuxer uses an input plugin to read the data and stores it
in pre-allocated buffers from the global buffer pool.
The buffers are then added to the audio or video stream fifo.
</P
><P
> From the other end of these fifos the audio and video decoder threads
consume the buffers and hand them over to the current audio or video
decoder plugin for decompression. These plugins then send the decoded
data to the output layer. The buffer holding the encoded
data is no longer needed and thus released to the global buffer pool.
</P
><P
> In the output layer, the video frames and audio samples pass through a
post plugin tree, which can apply effects or other operations to the data.
When reaching the output loops, frames and samples are enqueued to be
displayed, when the presentation time has arrived.
</P
><P
> A set of extra information travels with the data. Starting at the input and
demuxer level, where this information is generated, the data is attached to
the buffers as they wait in the fifo. The decoder loops copy the data to
a storage of their own. From there, every frame and audio buffer leaving
the stream layer is tagged with the data the decoder loop storage currently
holds.
</P
></DIV
><DIV
CLASS="SECT1"
><HR><H2
CLASS="SECT1"
><A
NAME="AEN461"
></A
>Plugin system</H2
><P
> The plugin system enables some of xine's most valuable features:
<P
></P
><UL
><LI
><P
> drop-in extensiability
</P
></LI
><LI
><P
> support parallel installation of multiple (incompatible) libxine versions
</P
></LI
><LI
><P
> support for multiple plugin directories
(<TT
CLASS="FILENAME"
>$prefix/lib/xine/plugins</TT
>,
<TT
CLASS="FILENAME"
>$HOME/.xine/plugins</TT
>, ...)
</P
></LI
><LI
><P
> support for recursive plugin directories
(plugins are found even in subdirectories of the plugin directories)
</P
></LI
><LI
><P
> version management
(On start, xine finds all plugins in its plugin (sub)directories and
chooses an appropriate version (usually the newest) for each plugin.)
</P
></LI
><LI
><P
> simplification
(Plugins don't have to follow any special naming convention,
and any plugin may contain an arbitrary subset of input, demuxer,
decoder or output plugins.)
</P
></LI
></UL
>
</P
><P
> Essentally, plugins are just shared objects, ie dynamic libraries. In
contrast to normal dynamic libraries, they are stored outside of the
system's library PATHs and libxine does its own bookkeeping, which
enables most advanced features mentioned above.
</P
><DIV
CLASS="SECT2"
><HR><H3
CLASS="SECT2"
><A
NAME="AEN480"
></A
>Plugin location and filesystem layout</H3
><P
> The primary goal for this new plugin mechanism was the need to support
simultaneous installation of several (most likely incompatible)
libxine versions without them overwriting each other's
plugins. Therefore, we have this simple layout:
</P
><P
> Plugins are installed below XINE_PLUGINDIR
(<TT
CLASS="FILENAME"
>/usr/local/lib/xine/plugins</TT
> by default).
Note that plugins are never directly installed into XINE_PLUGINDIR.
Instead, a separate subdirectory is created for each "plugin
provider". A plugin provider is equivalent with the exact version of
one source package. Typical examples include "xine-lib-0.9.11" or
"xine-vcdnav-1.0". Every source package is free to install an
arbitrary number of plugins in its own, private directory. If a
package installs several plugins, they may optionally be organized
further into subdirectories.
</P
><P
> So you will finally end up with something like this:
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="SCREEN"
> /usr/local/lib/xine/plugins
xine-lib-0.9.11
demux_mpeg_block.so
decode_mpeg.so
video_out_xv.so
...
xine-vcdnav-0.9.11
input_vcdnav.so
xine-lib-1.2
input
file.so
stdin_fifo.so
vcd.so
demuxers
fli.so
avi.so
...
decoders
ffmpeg.so
mpeg.so (may contain mpeg 1/2 audio and video decoders)
pcm.so
...
output
video_xv.so
audio_oss.so
...
xine-lib-3.0
avi.so (avi demuxer)
mpeg.so (contains mpeg demuxers and audio/video decoders)
video_out_xv.so (Xv video out)
...</PRE
></TD
></TR
></TABLE
>
</P
><P
> As you can see, every package is free to organize plugins at will
below its own plugin provider directory.
Additionally, administrators may choose to put plugins directly into
XINE_PLUGINDIR, or in a "local" subdirectory.
Users may wish to put additional plugins in ~/.xine/plugins/.
Again, there may be subdirectories to help organize the plugins.
</P
><P
> The default value for XINE_PLUGINDIR can be obtained using the
<B
CLASS="COMMAND"
>xine-config --plugindir</B
> command.
</P
></DIV
><DIV
CLASS="SECT2"
><HR><H3
CLASS="SECT2"
><A
NAME="AEN490"
></A
>Plugin Content: What's inside the .so?</H3
><P
> Each plugin library (.so file) contains an arbitrary number of (virtual)
plugins. Typically, it will contain exactly one plugin. However, it
may be useful to put a set of related plugins in one library, so they
can share common code.
</P
><P
> First of all, what is a virtual plugin?
A virtual plugin is essentially a structure that is defined by the
xine engine. This structure typically contains lots of function
pointers to the actual API functions.
For each plugin API, there are several API versions, and each API
version may specify a new, incompatible structure. Therefore, it is
essential that only those plugins are loaded that support current
libxine's API, so the .so file needs a plugin list that
provides libxine with the version information, even before it tries to
load any of the plugins.
</P
><P
> This plugin list is held in an array named <TT
CLASS="VARNAME"
>xine_plugin_info</TT
>":
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> plugin_info_t xine_plugin_info[] = {
/* type, API, "name", version, special_info, init_function */
{ PLUGIN_DEMUX, 20, "flac", XINE_VERSION_CODE, NULL, demux_flac_init_class },
{ PLUGIN_AUDIO_DECODER, 13, "flacdec", XINE_VERSION_CODE, &dec_info_audio, init_plugin },
{ PLUGIN_NONE, 0, "", 0, NULL, NULL }
};</PRE
></TD
></TR
></TABLE
>
</P
><P
> The structure of xine_plugin_info may <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>never</I
></SPAN
> be changed.
If it ever needs to be changed, it must be renamed to avoid
erraneous loading of incompatible plugins.
</P
><P
> <TT
CLASS="VARNAME"
>xine_plugin_info</TT
> can contain any number of plugins
and must be terminated with a <SPAN
CLASS="TYPE"
>PLUGIN_NONE</SPAN
> entry. Available plugin
types are:
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> #define PLUGIN_NONE 0
#define PLUGIN_INPUT 1
#define PLUGIN_DEMUX 2
#define PLUGIN_AUDIO_DECODER 3
#define PLUGIN_VIDEO_DECODER 4
#define PLUGIN_SPU_DECODER 5
#define PLUGIN_AUDIO_OUT 6
#define PLUGIN_VIDEO_OUT 7
#define PLUGIN_POST 8</PRE
></TD
></TR
></TABLE
>
</P
><P
> The plugin version number is generated from xine-lib's version number
like this: MAJOR * 10000 + MINOR * 100 + SUBMINOR.
This is not required, but it's an easy way to ensure that the version
increases for every release.
</P
><P
> Every entry in <TT
CLASS="VARNAME"
>xine_plugin_info</TT
> has an initialization
function for the plugin class context.
This function returns a pointer to freshly allocated (typically
via <TT
CLASS="FUNCTION"
>malloc()</TT
>) structure containing mainly function
pointers; these are the "methods" of the plugin class.
</P
><P
> The "plugin class" is not what we call to do the job yet (like decoding
a video or something), it must be instantiated. One reason for having the
class is to hold any global settings that must be accessed by every
instance. Remember that xine library is multistream capable: multible
videos can be decoded at the same time, thus several instances of the
same plugin are possible.
</P
><P
> If you think this is pretty much an object-oriented aproach,
then you're right.
</P
><P
> A fictitious file input plugin that supports input plugin API 12 and
13, found in xine-lib 2.13.7 would then define this plugin list:
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> #include <xine/plugin.h>
...
plugin_t *init_api12(void) {
input_plugin_t *this;
this = malloc(sizeof(input_plugin_t));
...
return (plugin_t *)this;
}
/* same thing, with different initialization for API 13 */
const plugin_info_t xine_plugin_info[] = {
{ PLUGIN_INPUT, 12, "file", 21307, init_api12 },
{ PLUGIN_INPUT, 13, "file", 21307, init_api13 },
{ PLUGIN_NONE, 0, "", 0, NULL }
}</PRE
></TD
></TR
></TABLE
>
This input plugin supports two APIs, other plugins might provide a
mixture of demuxer and decoder plugins that belong together somehow
(ie. share common code).
</P
><P
> You'll find exact definitions of public functions and plugin structs
in the appropriate header files for each plugin type:
<TT
CLASS="FILENAME"
>input/input_plugin.h</TT
> for input plugins,
<TT
CLASS="FILENAME"
>demuxers/demux.h</TT
> for demuxer plugins,
<TT
CLASS="FILENAME"
>xine-engine/video_decoder.h</TT
> for video decoder plugins,
<TT
CLASS="FILENAME"
>xine-engine/audio_decoder.h</TT
> for audio decoder plugins,
<TT
CLASS="FILENAME"
>xine-engine/post.h</TT
> for post plugins,
<TT
CLASS="FILENAME"
>xine-engine/video_out.h</TT
> for video out plugins,
<TT
CLASS="FILENAME"
>xine-engine/audio_out.h</TT
> for audio out plugins.
Additional information will also be given in the dedicated sections below.
</P
><P
> Many plugins will need some additional "private" data fields.
These should be simply added at the end of the plugin structure.
For example a demuxer plugin called "foo" with two private
fields "xine" and "count" may have a plugin structure declared in
the following way:
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> typedef struct {
/* public fields "inherited" from demux.h */
demux_plugin_t demux_plugin;
xine_t *xine;
int count;
} demux_foo_t;</PRE
></TD
></TR
></TABLE
>
</P
><P
> The plugin would then access public members via the
<TT
CLASS="VARNAME"
>demux_plugin</TT
> field and private fields directly.
</P
><P
> Summary: Plugins consist of two C-style classes, each representing a different context.
<P
></P
><UL
><LI
><P
> The first is the so called "plugin class" context. This is a singleton context,
which means it will exist either not at all or at most once per xine context.
This plugin class context is a C-style class which is subclassing the related
class from the xine plugin headers. This contains functions, which are
independent of the actual instance of the plugin. Most prominently, it contains
a factory method to instantiate the next context.
</P
></LI
><LI
><P
> The second context is the instance context. This is another C-style class, which
is constructed and disposed withing the plugin class context. This one does
the actual work and subclasses the related plugin struct from the xine plugin
headers. It is instantiated for every separate running instance of the plugin
</P
></LI
></UL
>
</P
></DIV
></DIV
><DIV
CLASS="SECT1"
><HR><H2
CLASS="SECT1"
><A
NAME="AEN529"
></A
>What is this metronom thingy?</H2
><P
> Metronom serves two purposes:
<P
></P
><UL
><LI
><P
> Generate vpts (virtual presentation time stamps) from pts (presentation time stamps)
for a/v output and synchronization.
</P
></LI
><LI
><P
> Provide a master clock (system clock reference, scr), possibly provided
by external scr plugins (this can be used if some hardware decoder or network
server dictates the time).
</P
></LI
></UL
>
</P
><P
> pts/vpts values are given in 1/90000 sec units. pts values in mpeg streams
may wrap (that is, return to zero or any other value without further notice),
can be missing on some frames or (for broken streams) may "dance" around
the correct values. Metronom therefore has some heuristics built-in to generate
clean vpts values which can then be used in the output layers to schedule audio/video
output.
</P
><P
> The heuristics used in metronom have always been a field of research. Current metronom's
implementation <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>tries</I
></SPAN
> to stick to pts values as reported from demuxers,
that is, vpts may be obtained by a simple operation of vpts = pts + <TT
CLASS="VARNAME"
>vpts_offset</TT
>,
where <TT
CLASS="VARNAME"
>vpts_offset</TT
> takes into account any wraps. Whenever pts is zero,
metronom will estimate vpts based on previous values. If a difference is found between the
estimated and calculated vpts values by above formula, it will be smoothed by using a
"drift correction".
</P
></DIV
><DIV
CLASS="SECT1"
><HR><H2
CLASS="SECT1"
><A
NAME="AEN542"
></A
>How does xine synchronize audio and video?</H2
><P
> Every image frame or audio buffer leaving decoder is tagged by metronom with
a vpts information. This will tell video_out and audio_out threads when that
data should be presented. Usually there isn't a significative delay associated
with video driver, so we expect it to get on screen at the time it's
delivered for drawing. Unfortunately the same isn't true for audio: all sound
systems implement some amount of buffering (or fifo), any data being send to it
<SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>now</I
></SPAN
> will only get played some time in future. audio_out thread
must take this into account for making perfect A-V sync by asking the sound latency
to audio driver.
</P
><P
> Some audio drivers can't tell the current delay introduced in playback. This is
especially true for most sound servers like ESD or aRts and explain why in such
cases the sync is far from perfect.
</P
><P
> Another problem xine must handle is the sound card clock drift. vpts are
compared to the system clock (or even to a different clock provided by a scr plugin)
for presentation but sound card is sampling audio by it's own clocking
mechanism, so a small drift may occur. As the playback goes on this
error will accumulate possibly resulting in audio gaps or audio drops. To avoid that
annoying effect, two countermeasures are available (switchable with xine config
option <TT
CLASS="PARAMETER"
><I
>audio.av_sync_method</I
></TT
>):
<P
></P
><UL
><LI
><P
> The small sound card errors are feedbacked to metronom. The details
are given by <TT
CLASS="FILENAME"
>audio_out.c</TT
> comments:
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> /* By adding gap errors (difference between reported and expected
* sound card clock) into metronom's vpts_offset we can use its
* smoothing algorithms to correct sound card clock drifts.
* obs: previously this error was added to xine scr.
*
* audio buf ---> metronom --> audio fifo --> (buf->vpts - hw_vpts)
* (vpts_offset + error) gap
* <---------- control --------------|
*
* Unfortunately audio fifo adds a large delay to our closed loop.
*
* These are designed to avoid updating the metronom too fast.
* - it will only be updated 1 time per second (so it has a chance of
* distributing the error for several frames).
* - it will only be updated 2 times for the whole audio fifo size
* length (so the control will wait to see the feedback effect)
* - each update will be of gap/SYNC_GAP_RATE.
*
* Sound card clock correction can only provide smooth playback for
* errors < 1% nominal rate. For bigger errors (bad streams) audio
* buffers may be dropped or gaps filled with silence.
*/</PRE
></TD
></TR
></TABLE
>
</P
></LI
><LI
><P
> The audio is stretched or squeezed a slight bit by resampling, thus compensating
the drift: The next comment in <TT
CLASS="FILENAME"
>audio_out.c</TT
> explains:
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="90%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> /* Alternative for metronom feedback: fix sound card clock drift
* by resampling all audio data, so that the sound card keeps in
* sync with the system clock. This may help, if one uses a DXR3/H+
* decoder board. Those have their own clock (which serves as xine's
* master clock) and can only operate at fixed frame rates (if you
* want smooth playback). Resampling then avoids A/V sync problems,
* gaps filled with 0-frames and jerky video playback due to different
* clock speeds of the sound card and DXR3/H+.
*/</PRE
></TD
></TR
></TABLE
>
</P
></LI
></UL
>
</P
></DIV
><DIV
CLASS="SECT1"
><HR><H2
CLASS="SECT1"
><A
NAME="OSD"
></A
>Overlays and OSD</H2
><P
> The roots of xine overlay capabilities are DVD subpictures and subtitles support
(also known as 'spu'). The DVD subtitles are encoded in a RLE (Run Length Encoding - the
most simple compressing technique) format, with a palette of colors and transparency
levels. You probably thought that subtitles were just simple text saved into DVDs, right?
Wrong, they are bitmaps.
</P
><P
> In order to optimize to the most common case, xine's internal format for screen overlays
is a similar representation to the 'spu' data. This brings not only performance
benefit (since blending functions may skip large image areas due to RLE) but also
compatibility: it's possible to reencode any xine overlay to the original spu format
for displaying with mpeg hardware decoders like DXR3.
</P
><P
> Displaying subtitles requires the ability to sync them to the video stream. This
is done using the same kind of pts/vpts stuff of a-v sync code. DVD subtitles,
for example, may request: show this spu at pts1 and hide it at pts2. This brings the
concept of the 'video overlay manager', that is a event-driven module for managing
overlay's showing and hiding.
</P
><P
> The drawback of using internal RLE format is the difficulty in manipulating it
as graphic. To overcome that we created the 'OSD renderer', where OSD stands
for On Screen Display just like in TV sets. The osd renderer is a module
providing simple graphic primitives (lines, rectagles, draw text etc) over
a "virtual" bitmap area. Everytime we want to show that bitmap it will
be RLE encoded and sent to the overlay manager for displaying.
</P
><DIV
CLASS="MEDIAOBJECT"
><P
><IMG
SRC="overlays.png"><DIV
CLASS="CAPTION"
><P
>overlays architecture</P
></DIV
></P
></DIV
><DIV
CLASS="SECT2"
><HR><H3
CLASS="SECT2"
><A
NAME="AEN571"
></A
>Overlay Manager</H3
><P
> The overlay manager interface is available to any xine plugin. It's a bit unlikely
to be used directly, anyway here's a code snippet for enqueueing an overlay for
displaying:
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> video_overlay_event_t event;
event.object.handle = this->video_overlay->get_handle(this->video_overlay,0);
memset(this->event.object.overlay, 0, sizeof(*this->event.object.overlay));
/* set position and size for this overlay */
event.object.overlay->x = 0;
event.object.overlay->y = 0;
event.object.overlay->width = 100;
event.object.overlay->height = 100;
/* clipping region is mostly used by dvd menus for highlighting buttons */
event.object.overlay->clip_top = 0;
event.object.overlay->clip_bottom = image_height;
event.object.overlay->clip_left = 0;
event.object.overlay->clip_right = image_width;
/* the hard part: provide a RLE image */
event.object.overlay->rle = your_rle;
event.object.overlay->data_size = your_size;
event.object.overlay->num_rle = your_rle_count;
/* palette must contain YUV values for each color index */
memcpy(event.object.overlay->clip_color, color, sizeof(color));
/* this table contains transparency levels for each color index.
0 = completely transparent, 15 - completely opaque */
memcpy(event.object.overlay->clip_trans, trans, sizeof(trans));
/* set the event type and time for displaying */
event.event_type = EVENT_SHOW_SPU;
event.vpts = 0; /* zero is a special vpts value, it means 'now' */
video_overlay->add_event(video_overlay, &event);</PRE
></TD
></TR
></TABLE
>
</P
></DIV
><DIV
CLASS="SECT2"
><HR><H3
CLASS="SECT2"
><A
NAME="AEN575"
></A
>OSD Renderer</H3
><P
> OSD is a general API for rendering stuff over playing video. It's available both
to xine plugins and to frontends.
</P
><P
> The first thing you need is to allocate a OSD object for drawing from the
renderer. The code below allocates a 300x200 area. This size can't be changed
during the lifetime of a OSD object, but it's possible to place it anywhere
over the image.
</P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> osd_object_t osd;
osd = this->osd_renderer->new_object(osd_renderer, 300, 200);</PRE
></TD
></TR
></TABLE
><P
> Now we may want to set font and color for text rendering. Although we will
refer to fonts over this document, in fact the OSD can be any kind of bitmap. Font
files are searched and loaded during initialization from
<TT
CLASS="FILENAME"
>$prefix/share/xine/fonts/</TT
> and <TT
CLASS="FILENAME"
>~/.xine/fonts</TT
>.
There's a sample utility to convert truetype fonts at
<TT
CLASS="FILENAME"
>xine-lib/misc/xine-fontconv.c</TT
>. Palette may be manipulated directly,
however most of the time it's convenient to use pre-defined text palettes.
</P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> /* set sans serif 24 font */
osd_renderer->set_font(osd, "sans", 24);
/* copy pre-defined colors for white, black border, transparent background to
starting at the index used by the first text palette */
osd_renderer->set_text_palette(osd, TEXTPALETTE_WHITE_BLACK_TRANSPARENT, OSD_TEXT1);
/* copy pre-defined colors for white, no border, translucid background to
starting at the index used by the second text palette */
osd_renderer->set_text_palette(osd, TEXTPALETTE_WHITE_NONE_TRANSLUCID, OSD_TEXT2);</PRE
></TD
></TR
></TABLE
><P
> Now render the text and show it:
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> osd_renderer->render_text(osd, 0, 0, "white text, black border", OSD_TEXT1);
osd_renderer->render_text(osd, 0, 30, "white text, no border", OSD_TEXT2);
osd_renderer->show(osd, 0); /* 0 stands for 'now' */</PRE
></TD
></TR
></TABLE
>
</P
><P
> There's a 1:1 mapping between OSD objects and overlays, therefore the
second time you send an OSD object for displaying it will actually substitute
the first image. By using set_position() function we can move overlay
over the video.
</P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> for( i=0; i < 100; i+=10 ) {
osd_renderer->set_position(osd, i, i );
osd_renderer->show(osd, 0);
sleep(1);
}
osd_renderer->hide(osd, 0);</PRE
></TD
></TR
></TABLE
><P
> For additional functions please check osd.h or the public header.
</P
><DIV
CLASS="SECT3"
><HR><H4
CLASS="SECT3"
><A
NAME="AEN590"
></A
>OSD palette notes</H4
><P
> The palette functions demand some additional explanation, skip this if you
just want to write text fast without worring with details! :)
</P
><P
> We have a 256-entry palette, each one defining yuv and transparency levels.
Although xine fonts are bitmaps and may use any index they want, we have
defined a small convention:
</P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> /*
Palette entries as used by osd fonts:
0: not used by font, always transparent
1: font background, usually transparent, may be used to implement
translucid boxes where the font will be printed.
2-5: transition between background and border (usually only alpha
value changes).
6: font border. if the font is to be displayed without border this
will probably be adjusted to font background or near.
7-9: transition between border and foreground
10: font color (foreground)
*/</PRE
></TD
></TR
></TABLE
><P
> The so called 'transitions' are used to implement font anti-aliasing. That
convention requires that any font file must use only the colors from 1 to 10.
When we use the set_text_palette() function we are just copying 11 palette
entries to the specified base index.
</P
><P
> That base index is the same we pass to render_text() function to use the
text palette. With this scheme is possible to have several diferent text
colors at the same time and also draw fonts over custom background.
</P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> /* obtains size the text will occupy */
renderer->get_text_size(osd, text, &width, &height);
/* draws a box using font background color (translucid) */
renderer->filled_rect(osd, x1, y1, x1+width, y1+height, OSD_TEXT2 + 1);
/* render text */
renderer->render_text(osd, x1, y1, text, OSD_TEXT2);</PRE
></TD
></TR
></TABLE
></DIV
><DIV
CLASS="SECT3"
><HR><H4
CLASS="SECT3"
><A
NAME="AEN598"
></A
>OSD text and palette FAQ</H4
><P
> Q: What is the format of the color palette entries?
</P
><P
> A: It's the same as used by overlay blending code (YUV).
</P
><P
> Q: What is the relation between a text palette and a palette
I set with xine_osd_set_palette?
</P
><P
> A: xine_osd_set_palette will set the entire 256 color palette
to be used when we blend the osd image.
"text palette" is a sequence of 11 colors from palette to be
used to render text. that is, by calling osd_render_text()
with color_base=100 will render text using colors 100-110.
</P
><P
> Q: Can I render text with colors in my own palette?
</P
><P
> A: Sure. Just pass the color_base to osd_render_text()
</P
><P
> Q: Has a text palette change effects on already drawed text?
</P
><P
> A: osd_set_text_palette() will overwrite some colors on palette
with pre-defined ones. So yes, it will change the color
on already drawed text (if you do it before calling osd_show,
of course).
If you don't want to change the colors of drawed text just
use different color_base values.
</P
><P
> Q: What about the shadows of osd-objects? Can I turn them off
or are they hardcoded?
</P
><P
> A: osd objects have no shadows by itself, but fonts use 11
colors to produce an anti-aliased effect.
if you set a "text palette" with entries 0-9 being transparent
and 10 being foreground you will get rid of any borders or
anti-aliasing.
</P
></DIV
></DIV
></DIV
><DIV
CLASS="SECT1"
><HR><H2
CLASS="SECT1"
><A
NAME="AEN610"
></A
>MRLs</H2
><P
> This section defines a draft for a syntactic specification of MRLs as
used by xine-lib. The language of MRLs is designed to be a true subset
of the language of URIs as given in RFC2396. A type 2 grammar for the
language of MRLs is given in EBNF below.
</P
><P
> Semantically, MRLs consist of two distinct parts that are evaluated by
different components of the xine architecture. The first part,
derivable from the symbol <input_source> in the given grammar, is
completely handed to the input plugins, with input plugins signaling
if they can handle the MRL.
</P
><P
> The second part, derivable from <stream_setup> and delimited from the
first by a crosshatch ('#') contains parameters that modify the
initialization and playback behaviour of the stream to which the MRL
is passed. The possible parameters are mentioned in the manpage to
xine-ui.
</P
><P
> The following definition should be regarded as a guideline only.
Of course any given input plugin only understands a subset of all
possible MRLs. On the other hand, invalid MRLs according to this
definition might be understood for convenience reasons.
Some user awareness is required at this point.
</P
><P
> EBNF grammar for MRLs:
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> <mrl> ::= <input_source>[#<stream_setup>]
<input_source> ::= (<absolute_mrl>|<relative_mrl>)
<absolute_mrl> ::= <input>:(<net_path>|<abs_path>)[?<query>]
<relative_mrl> ::= (<abs_path>|<rel_path>)
<net_path> ::= //<authority>[<abs_path>]
<abs_path> ::= /<path_segments>
<rel_path> ::= <rel_segment>[<abs_path>]
<rel_segment> ::= <rel_char>{<rel_char>}
<rel_char> ::= (<unreserved>|<escaped>|;|@|&|=|+|$|,)
<input> ::= <alpha>{(<alpha>|<digit>|+|-|.)}
<authority> ::= (<server>|<reg_name>)
<server> ::= [[<userinfo>@]<host>[:<port>]]
<userinfo> ::= {(<unreserved>|<escaped>|;|:|&|=|+|$|,)}
<host> ::= (<hostname>|<ipv4_address>)
<hostname> ::= {<domainlabel>.}<toplabel>[.]
<domainlabel> ::= (<alphanum>|<alphanum>{(<alphanum>|-)}<alphanum>)
<toplabel> ::= (<alpha>|<alpha>{(<alphanum>|-)}<alphanum>)
<ipv4_address> ::= <digit>{<digit>}.<digit>{<digit>}.<digit>{<digit>}.<digit>{<digit>}
<port> ::= {<digit>}
<reg_name> ::= <reg_char>{<reg_char>}
<reg_char> ::= (<unreserved>|<escaped>|;|:|@|&|=|+|$|,)
<path_segments> ::= <segment>{/<segment>}
<segment> ::= {<path_char>}{;<param>}
<param> ::= {<path_char>}
<path_char> ::= (<unreserved>|<escaped>|:|@|&|=|+|$|,)
<query> ::= {<mrl_char>}
<stream_setup> ::= <stream_option>;{<stream_option>}
<stream_option> ::= (<configoption>|<engine_option>|novideo|noaudio|nospu)
<configoption> ::= <configentry>:<configvalue>
<configentry> ::= <unreserved>{<unreserved>}
<configvalue> ::= <conf_char>{<conf_char>}
<engine_option> ::= <unreserved>{<unreserved>}:<stream_char>{<stream_char>}
<stream_char> ::= (<unreserved>|<escaped>|:|@|&|=|+|$|,)
<mrl_char> ::= (<reserved>|<unreserved>|<escaped>)
<reserved> ::= (;|/|?|:|@|&|=|+|$|,)
<unreserved> ::= (<alphanum>|<mark>)
<mark> ::= (-|_|.|!|~|*|'|(|))
<escaped> ::= %<hex><hex>
<hex> ::= (<digit>|A|B|C|D|E|F|a|b|c|d|e|f)
<alphanum> ::= (<alpha>|<digit>)
<alpha> ::= (<lowalpha>|<upalpha>)
<lowalpha> ::= (a|b|c|d|e|f|g|h|i|j|k|l|m|n|o|p|q|r|s|t|u|v|w|x|y|z)
<upalpha> ::= (A|B|C|D|E|F|G|H|I|J|K|L|M|N|O|P|Q|R|S|T|U|V|W|X|Y|Z)
<digit> ::= (0|1|2|3|4|5|6|7|8|9)</PRE
></TD
></TR
></TABLE
>
</P
></DIV
></DIV
><DIV
CLASS="CHAPTER"
><HR><H1
><A
NAME="STREAM"
></A
>Chapter 5. xine's stream layer</H1
><DIV
CLASS="SECT1"
><H2
CLASS="SECT1"
><A
NAME="AEN620"
></A
>Input layer</H2
><P
> Many media players expect streams to be stored within files on
some local medium. In actual fact, media may be streamed over a
network (e.g. via HTTP or RTP), encoded onto a specialized medium
(e.g. DVD), etc. To allow you to access all this media, xine supports
the concept of an "input plugin". The tasks performed by an
input plugin are:
<P
></P
><UL
><LI
><P
> Validation of Media Resource Locators (MRLs).
</P
></LI
><LI
><P
> MRL specific session management (e.g. opening and closing local files).
</P
></LI
><LI
><P
> Reading blocks/specific numbers of bytes from the input device.
</P
></LI
></UL
>
</P
><P
> In addition to these tasks, the input plugin may keep track of some
input device-specific state information (e.g. a DVD plugin may keep
track of navigational state data such as current title/chapter).
</P
><P
> There are two classes of input device which xine recognizes.
Byte-oriented devices can, upon request, return an arbitary
non-zero number of bytes from a stream. Examples of such devices
are files or network streams. Block-oriented devices, however, have
a prefered block or "frame"-size. An example of such a device is
a DVD where data is stored in logical blocks of 2048 bytes. One may
pass the hint to xine that the plugin is block-oriented by setting the
INPUT_CAP_BLOCK capability. Note that this is only a hint and
xine does not guarantee that all requests to the plugin will
be purely block based.
</P
><DIV
CLASS="SECT2"
><HR><H3
CLASS="SECT2"
><A
NAME="AEN632"
></A
>Writing a xine input plugin</H3
><P
> An input plugin provides API functions which allow the engine to
access the data source the plugin encapsulates. The input plugin API
is declared in <TT
CLASS="FILENAME"
>input/input_plugin.h</TT
>.
</P
><P
> An input plugin exports a public function of the form:
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> void *input_init_plugin(xine_t *xine, void *data);</PRE
></TD
></TR
></TABLE
>
This function initializes an input plugin class object with the
following functions:
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> char *get_description(input_class_t *this_gen);</PRE
></TD
></TR
></TABLE
>
This function returns a plaintext, one-line string describing the plugin.
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> char *get_identifier(input_class_t *this_gen);</PRE
></TD
></TR
></TABLE
>
This function returns a shorter identifier describing the plugin.
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> xine_mrl_t **get_dir(input_class_t *this_gen, const char *filename, int *nFiles);</PRE
></TD
></TR
></TABLE
>
Retrieves a directory listing from the plugin. This function is optional.
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> char **get_autoplay_list(input_class_t *this_gen, int *num_files);</PRE
></TD
></TR
></TABLE
>
Retrieves the autoplay playlist from the plugin. This function is optional.
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> int eject_media(input_class_t *this_gen);</PRE
></TD
></TR
></TABLE
>
Ejects the medium. This function is optional.
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> void dispose(input_class_t *this_gen);</PRE
></TD
></TR
></TABLE
>
This function frees the memory used by the input plugin class object.
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> input_plugin_t *get_instance(input_class_t *class_gen, xine_stream_t *stream, const char *mrl);</PRE
></TD
></TR
></TABLE
>
The plugin should try, if it can handle the specified MRL and return an
instance of itself if so. If not, NULL should be returned.
Note that input plugins are not guaranteed to be queried
in anay particular order and the first input plugin to claim an MRL
gets control so try not to duplicate MRLs already found within xine.
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> int open(input_plugin_t *this_gen);</PRE
></TD
></TR
></TABLE
>
You should do any device-specific initialisation within this function.
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> uint32_t get_capabilities(input_plugin_t *this_gen);</PRE
></TD
></TR
></TABLE
>
Returns a bit mask describing the input device's capabilities.
You may logically OR the <TT
CLASS="VARNAME"
>INPUT_CAP_*</TT
> constants together to get
a suitable bit-mask (via the '|' operator).
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> off_t read(input_plugin_t *this_gen, char *buf, off_t nlen);</PRE
></TD
></TR
></TABLE
>
Reads a specified number of bytes into a buffer and returns the number of bytes actually copied.
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> buf_element_t *read_block(input_plugin_t *this_gen, fifo_buffer_t *fifo, off_t len);</PRE
></TD
></TR
></TABLE
>
Should the input plugin set the block-oriented hint and if the
demuxer supports it, this function will be called to read a block directly
into a xine buffer from the buffer pool.
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> off_t seek(input_plugin_t *this_gen, off_t offset, int origin);</PRE
></TD
></TR
></TABLE
>
This function is called by xine when it is required that subsequent
reads come from another part of the stream.
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> off_t get_current_pos(input_plugin_t *this_gen);</PRE
></TD
></TR
></TABLE
>
Returns the current position within a finite length stream.
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> off_t get_length(input_plugin_t *this_gen);</PRE
></TD
></TR
></TABLE
>
Similarly this function returns the length of the stream.
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> uint32_t get_blocksize(input_plugin_t *this_gen);</PRE
></TD
></TR
></TABLE
>
Returns the device's prefered block-size if applicable.
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> char *get_mrl(input_plugin_t *this_gen);</PRE
></TD
></TR
></TABLE
>
Returns the current MRL.
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> int get_optional_data(input_plugin_t *this_gen, void *data, int data_type);</PRE
></TD
></TR
></TABLE
>
This function allows the input to advertise extra information that is
not available through other API functions. See <TT
CLASS="VARNAME"
>INPUT_OPTIONAL_*</TT
> defines.
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> void dispose(input_plugin_t *this_gen);</PRE
></TD
></TR
></TABLE
>
This function closes all resources and frees the input_plugin_t object.
</P
></DIV
></DIV
><DIV
CLASS="SECT1"
><HR><H2
CLASS="SECT1"
><A
NAME="AEN676"
></A
>Demuxer layer</H2
><P
> This section is designed to familiarize a programmer with general demuxer
concepts and how they apply to the xine multimedia library.
</P
><DIV
CLASS="SECT2"
><HR><H3
CLASS="SECT2"
><A
NAME="AEN679"
></A
>Introduction to demuxer theory</H3
><P
> xine's demuxer layer is responsible for taking apart multimedia files or
streams so that the engine can decode them and present them to the user.
"Demuxer" is short for demultiplexor, which is the opposite of
multiplexing. This refers to the process of combining 2 or more things
into one. Multimedia streams usually, at a minimum, multiplex an audio
stream and a video stream together into one stream. Sometimes, there are
multiple audio streams (e.g., for multiple language tracks). Sometimes,
there is a subtitle data stream multiplexed into the multimedia stream.
</P
><P
> There are many different multimedia formats in existence and there are
varying strategies for demuxing different types of multimedia files.
Formats in the MPEG family, for example, are designed to allow easy
playback from almost any place within the file. Many formats cannot deal
with this circumstance and at least need to be demuxed from the beginning
of the stream and played through to the end. Some formats, such as MPEG and
AVI, have marker information before every chunk in the stream. Other
formats, such as Apple Quicktime, are required to have a master index that
contains all information for taking apart a file. Many game-oriented
multimedia formats are designed strictly for playing from start to finish
without any regard to random seeking within the file.
</P
></DIV
><DIV
CLASS="SECT2"
><HR><H3
CLASS="SECT2"
><A
NAME="AEN683"
></A
>Input considerations</H3
><P
> A xine demuxer interacts with xine's input layer in order to receive
data. The underlying input plugin might be a file, a network stream, or
a block-oriented disc storage device like a DVD. A file input offers the
most flexibility in being able to read either blocks of data or individual
bytes, and being able to seek freely. Other input plugins may not allow the
demuxer to seek (such as stdin or certain network streams). Some input
plugins only allow the demuxer to read blocks of data and not individual
bytes (such as the CD-DA input plugin). The demuxer needs to check the
capabilities of the underlying input plugin before attempting to seek
around.
</P
></DIV
><DIV
CLASS="SECT2"
><HR><H3
CLASS="SECT2"
><A
NAME="AEN686"
></A
>Seeking Policy</H3
><P
> If possible, it is desirable that a demuxer can seek randomly through
the stream. This is easier for some file formats and essentially impossible
for other formats. xine's seeking API function allows a seek target to be
specified in terms of stream offset from 0, or time in milliseconds from 0.
Offset-based seeking is useful for seek bars in multimedia applications.
Time-based seeking is useful for specifying, e.g., a 1-minute jump forward
or backward in a stream.
</P
><P
> If a multimedia stream has video, there generally needs to be a way to
identify keyframes in the stream in order to facilitate seeking. Many
game-oriented formats fall over in this area as they carry no keyframe
information aside from the implicit assumption that the first frame is a
keyframe.
</P
><P
> In a stream with video, a seek operation should always jump to a keyframe.
xine Policy: When the seek target is between 2 keyframes, jump to the
earlier keyframe. E.g., if there are keyframes at stream offsets 10000 and
20000, and the user requests a seek to offset 18000, choose the keyframe
at offset 10000.
</P
><P
> Note that there can be difficulties when the audio and video streams are
not tightly interleaved. In many formats, the audio frames are several
time units ahead of the video frames for the purpose of pre-buffering.
This is a typical scenario in the middle of a stream:
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> audio frame @ time 10
video frame @ time 8
audio frame @ time 11
video frame @ time 9
audio frame @ time 12
keyframe @ time 10
audio frame @ time 13</PRE
></TD
></TR
></TABLE
>
If the demuxer seeks to the keyframe @ time 10, the next audio chunk will
have a timestamp of 13, which is well ahead of where the video is. While
the xine engine will eventually recover, it will make playback choppy for
a few seconds after the seek. One strategy for dealing with this situation
is to seek back to the nearest keyframe before the requested seek and then
seek back to find the audio frame with the nearest timestamp before the
keyframe. In this example, that would mean seeking back to [af@time 10].
Then, demux the chunks in order, but skip the video frames until the next
keyframe is encountered.
</P
></DIV
><DIV
CLASS="SECT2"
><HR><H3
CLASS="SECT2"
><A
NAME="AEN693"
></A
>Writing a xine demuxer</H3
><P
> A demuxer plugin provides API functions which allow the engine to
initialize demuxing, dispatch data chunks to the engine, seek within the
stream, get the stream length, among other functions. The demuxer API
is declared in <TT
CLASS="FILENAME"
>demuxers/demux.h</TT
>.
</P
><P
> Writing a new xine demuxer is largely a process of using other demuxers as
references and understanding how they interact with the engine. This
section will give a brief overview of each API function.
</P
><P
> A demuxer plugin exports a public function of the form:
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> void *demux_wc3movie_init_plugin(xine_t *xine, void *data);</PRE
></TD
></TR
></TABLE
>
This function initializes a demuxer plugin class object with 6
demuxer-specific functions. These functions mainly provide information
that a frontend can use to build user-friendly features. These functions
include:
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> char *get_description(demux_class_t *this_gen);</PRE
></TD
></TR
></TABLE
>
This function returns a plaintext, one-line string describing the plugin.
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> char *get_identifier(demux_class_t *this_gen);</PRE
></TD
></TR
></TABLE
>
This function returns a shorter identifier describing the plugin.
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> char *get_extensions(demux_class_t *this_gen);</PRE
></TD
></TR
></TABLE
>
This function returns a string with the file extensions that this demuxer
is known to use. For example, Microsoft .WAV files use "wav". If there are
multiple known extensions, separate each extension with a space. For
example, Apple Quicktime has the extensions "mov qt mp4".
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> char *get_mimetypes(demux_class_t *this_gen)</PRE
></TD
></TR
></TABLE
>
This function returns a string with the MIME types that this demuxer is
known to use. Multiple MIME type specifications should be separated with a
semicolon (;). For example, Apple Quicktime uses several MIME types:
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> return "video/quicktime: mov,qt: Quicktime animation;"
"video/x-quicktime: mov,qt: Quicktime animation;"
"application/x-quicktimeplayer: qtl: Quicktime list;";</PRE
></TD
></TR
></TABLE
>
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> void class_dispose(demux_class_t *this_gen);</PRE
></TD
></TR
></TABLE
>
This function frees the memory used by the demuxer plugin class object.
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> demux_plugin_t *open_plugin(demux_class_t *class_gen, xine_stream_t *stream, input_plugin_t *input_gen);</PRE
></TD
></TR
></TABLE
>
This function is invoked by the xine engine to determine if the demuxer is
able to handle a particular multimedia stream. The engine can specify if
the demuxer is supposed to check the stream by content (validate the actual
stream data and see if it is of the expected type), by extension (check the
name of the MRL and see if the file extension is correct), or explicitly
(the engine is passing on a user request to force this demuxer to be used).
</P
><P
> NOTE: In the course of checking the stream by content, care must be taken
not to consume bytes out of a non-seekable stream. If the stream is
non-seekable, use the input plugin's preview buffer facility to get a cache
of the first few bytes. If the stream is seekable, reset the stream before
operating on the data (you do not know where some other demuxer left the
stream positioned).
</P
><P
> If the demuxer can handle the stream, it creates a new demux_plugin_t
structure and initializes the main demuxer functions which are called by
the engine to do the tough demuxing duty. These functions include:
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> void demux_send_headers(demux_plugin_t *this_gen);</PRE
></TD
></TR
></TABLE
>
This function generally reads the headers of the stream, does whatever it
has to do to figure out what audio and video codecs are used in the file,
and asks the xine engine to initialize the correct decoders with the
proper parameters (like width and height for video, sample rate and
channels for audio).
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> int demux_send_chunk(demux_plugin_t *this_gen);</PRE
></TD
></TR
></TABLE
>
This function reads data from the stream and sends it to the appropriate
decoder. This is where the bulk of the demuxing work is performed. Despite
the name, the function is actually free to send as much data as it wants
to, or as much as it can. A good policy is to send an entire chunk of
compressed audio or video data and then return. The chunk is likely large
enough that it will have to be broken up into multiple xine buffers. If
a chunk of audio is 20000 bytes large, and the engine is returning
4096-byte buffers, send 4 full buffers and 1 partial buffer to the audio
decoder and then return.
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> int demux_seek(demux_plugin_t *this_gen, off_t start_pos, int start_time);</PRE
></TD
></TR
></TABLE
>
This function is called by the engine to request stream repositioning.
This function should be implemented if possible. See the section on
"Seeking Policy" for more information. A seek operation should reposition
the demuxer's internal accounting variables to be ready to start
dispatching chunks from the new position when the xine engine calls
demux_send_chunk() again. If seeking is not feasible, the function quietly
returns and the demuxer's position is unaffected.
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> void demux_dispose(demux_plugin_t *this_gen);</PRE
></TD
></TR
></TABLE
>
This function frees the demux_plugin_t object.
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> int demux_get_status(demux_plugin_t *this_gen);</PRE
></TD
></TR
></TABLE
>
This function returns the current internal status of the demuxer. There
are 2 states: DEMUX_OK, for when the demuxer is demuxing or ready to demux,
and DEMUX_FINISHED, for when the demuxer has reached the end of the stream
or has encountered some sort of error.
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> int demux_get_stream_length(demux_plugin_t *this_gen);</PRE
></TD
></TR
></TABLE
>
This function returns the length (time duration) of the stream in
milliseconds. If the length of the stream cannot be determined, return 0.
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> uint32_t demux_get_capabilities(demux_plugin_t *this_gen);</PRE
></TD
></TR
></TABLE
>
This function returns an array of bit flags indicating special features of
the demuxer. See <TT
CLASS="VARNAME"
>DEMUX_CAP_*</TT
> defines.
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> int demux_get_optional_data(demux_plugin_t *this_gen, void *data, int data_type);</PRE
></TD
></TR
></TABLE
>
This function allows the demuxer to advertise extra information that is
not available through other API functions. See <TT
CLASS="VARNAME"
>DEMUX_OPTIONAL_*</TT
> defines.
</P
></DIV
><DIV
CLASS="SECT2"
><HR><H3
CLASS="SECT2"
><A
NAME="AEN733"
></A
>Buffer types</H3
><P
> Demuxer must send data to decoders using two fifos names <TT
CLASS="VARNAME"
>video_fifo</TT
>
and <TT
CLASS="VARNAME"
>audio_fifo</TT
>. Both are available at <TT
CLASS="VARNAME"
>stream</TT
>
level. The following code fragment shows how it's done.
</P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> buf_element_t *buf;
buf = stream->video_fifo->buffer_pool_alloc(stream->video_fifo);
buf->type = BUF_CONTROL_START;
stream->video_fifo->put(stream->video_fifo, buf);</PRE
></TD
></TR
></TABLE
><P
> Buffers must have set the <TT
CLASS="VARNAME"
>type</TT
> field as shown. All buffer types are
defined in <TT
CLASS="FILENAME"
>xine-engine/buffer.h</TT
>.
</P
><P
> The control buffer types are very important and must be sent by all kinds of demuxers.
They tell decoders to start/stop their operations and inform metronom about
discontinuities, either relative or absolute. There is also a reset buffer
type that must be sent when demuxers are seeking as a "warm restart" indication to
the decoders.
</P
><P
> To help finding out buffer types for known codecs, functions from <TT
CLASS="FILENAME"
>buffer_types.c</TT
>
may be used to convert "FOURCC" codes or audio format tags (as used in AVI files) to the xine
byffer type:
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> buf->type = fourcc_to_buf_video((void*)this->avi->bih.biCompression);</PRE
></TD
></TR
></TABLE
>
</P
></DIV
></DIV
><DIV
CLASS="SECT1"
><HR><H2
CLASS="SECT1"
><A
NAME="AEN747"
></A
>Decoder layer</H2
><P
> This section is designed to familiarize a programmer with basic audio
and video decoding concepts and how they apply to the xine decoder API.
</P
><DIV
CLASS="SECT2"
><HR><H3
CLASS="SECT2"
><A
NAME="AEN750"
></A
>Audio and video decoders</H3
><P
> Audio and video data requires an enormous amount of storage. Thus, the
raw data is encoded using a variety of compression techniques which
drastically reduces the amount of space required to transmit and store the
data. Before playback, the compressed data needs to be decoded.
</P
><P
> The process of decoding data is rather straightforward in a computer
science sense: An array of encoded data is fed into a decoder and the
decoder outputs an array of decoded data which is ready to be presented
to the user (either displayed on the screen or played through the
speakers).
</P
></DIV
><DIV
CLASS="SECT2"
><HR><H3
CLASS="SECT2"
><A
NAME="AEN754"
></A
>Video output formats</H3
><P
> Raw video data comes in a variety of formats, most commonly in RGB and
YUV. xine's output layer currently only accepts data in YV12 format (a.k.a.
YUV 4:2:0 planar) or YUY2 format (a.k.a. YUV 4:2:2 packed). If the output
format is a RGB space, the data must be converted to an acceptable YUV
format before being dispatched to the video output unit. xine has a number
of support functions to facilitate converting RGB to YUV.
</P
></DIV
><DIV
CLASS="SECT2"
><HR><H3
CLASS="SECT2"
><A
NAME="AEN757"
></A
>Audio output formats</H3
><P
> Raw audio data equates to uncompressed PCM audio. xine's audio output
modules expect 8-bit PCM data to be unsigned and 16-bit PCM data to be
signed and in little endian format. When there is more than one channel,
the channel data is interleaved. For example, stereo data is interleaved
as left sample, right sample: LRLRLRLR. If there are 4 or 6 channels, the
same interleaving applies: 123456123456.
</P
></DIV
><DIV
CLASS="SECT2"
><HR><H3
CLASS="SECT2"
><A
NAME="AEN760"
></A
>Writing a xine decoder</H3
><P
> Writing a new xine decoder for an audio or video format entails
accumulating a buffer of encoded data, performing the necessary operations
for decoding and then passing it on the appropriate output module. The
best reference for understanding the decoder API is the various decoding
modules available. In particular, xine has example video and audio
decoders named <TT
CLASS="FILENAME"
>src/libxinevdec/foovideo.c</TT
> and
<TT
CLASS="FILENAME"
>src/libxineadec/fooaudio.c</TT
>, respectively.
</P
><P
> This section will give a brief overview of each API function.
The decoder API is declared in <TT
CLASS="FILENAME"
>src/xine-engine/video_decoder.h</TT
>
and <TT
CLASS="FILENAME"
>src/xine-engine/audio_decoder.h</TT
>.
</P
><P
> A decoder plugin must, like every plugin, export a public array of
plugin_info_t types. The array usually has 2 entries: The first contains
the plugin information regarding the decoder and the second entry is
a terminating NULL entry. However, there may be more entries.
Each entry contains 6 fields:
<P
></P
><UL
><LI
><P
> <TT
CLASS="VARNAME"
>plugin type</TT
>: Either PLUGIN_VIDEO_DECODER or PLUGIN_AUDIO_DECODER.
</P
></LI
><LI
><P
> <TT
CLASS="VARNAME"
>API</TT
>: The plugin API revision that this plugin adheres to.
</P
></LI
><LI
><P
> <TT
CLASS="VARNAME"
>name</TT
>: A character string that identifies the plugin.
</P
></LI
><LI
><P
> <TT
CLASS="VARNAME"
>version</TT
>: #define'd as XINE_VERSION_CODE.
</P
></LI
><LI
><P
> <TT
CLASS="VARNAME"
>supported types</TT
>: A structure that defines the buffer types that this plugin can handle.
</P
></LI
><LI
><P
> <TT
CLASS="VARNAME"
>init function</TT
>: The function that the xine engine calls in order to initialize this decoder plugin.
</P
></LI
></UL
>
The supported types field is a decoder_info_t structure. This struct
combines a list of buffer types that the plugin can handle, along with
a relative default priority. The priority allows xine to have multiple
plugins that can handle one data type and the plugin with the highest
priority takes precedence. The code defines the default priority, which
can be overriden by the user.
The list of buffer types is an array of uint32_t types from the list of
buffer types defined in <TT
CLASS="FILENAME"
>src/xine-engine/buffer.h</TT
>.
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> void *init_plugin(xine_t *xine, void *data);</PRE
></TD
></TR
></TABLE
>
This function allocates a plugin class and initializes a set of functions
for the xine engine to invoke. These functions include:
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> char *get_identifier(video_decoder_class_t *this);</PRE
></TD
></TR
></TABLE
>
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> char *get_identifier(audio_decoder_class_t *this);</PRE
></TD
></TR
></TABLE
>
This function returns a brief character string identifying the plugin.
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> char *get_description(video_decoder_class_t *this);</PRE
></TD
></TR
></TABLE
>
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> char *get_description(audio_decoder_class_t *this);</PRE
></TD
></TR
></TABLE
>
This function returns a slightly longer description of the plugin.
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> void dispose_class(video_decoder_class_t *this);</PRE
></TD
></TR
></TABLE
>
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> void dispose_class(audio_decoder_class_t *this);</PRE
></TD
></TR
></TABLE
>
This function frees the resources allocated by the plugin class.
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> video_decoder_t *open_plugin(video_decoder_class_t *class_gen, xine_stream_t *stream);</PRE
></TD
></TR
></TABLE
>
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> audio_decoder_t *open_plugin(audio_decoder_class_t *class_gen, xine_stream_t *stream);</PRE
></TD
></TR
></TABLE
>
This function initializes the decoder plugin's private state. It also
initializes and returns either an audio_decoder_t or a video_decoder_t for
the engine. The decoder_t contains a number of functions that the plugin
invokes to handle data decoding. These functions include:
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> void decode_data(video_decoder_t *this_gen, buf_element_t *buf);</PRE
></TD
></TR
></TABLE
>
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> void decode_data(audio_decoder_t *this_gen, buf_element_t *buf);</PRE
></TD
></TR
></TABLE
>
This function performs the bulk of the decoding work. The xine engine
delivers buffers (xine_buffer_t data types) to this function and it is up
to this function to assemble the parts of the buffer, decode the data, and
send the decoded data to the proper output unit.
</P
><P
> A buffer has a <TT
CLASS="VARNAME"
>decoder_flags</TT
> field which can have
a number of flags set. The first buffer that a decoder receives ought
to have the BUF_FLAG_HEADER flag set. This indicates that the buffer
content contains the essential setup information for decoding
(width, height, etc. for video; sample rate, channels, etc. for audio).
</P
><P
> If the BUF_FLAG_HEADER flag is not set, the content of the buffer should
be accumulated in a private buffer until a buffer with a
BUF_FLAG_FRAME_END flag is set. This indicates that the entire chunk has
been transmitted to the decoder and is ready to be decoded. Fetch either
an empty video frame or audio buffer from the appropriate output unit. Perform
the appropriate decoding operations and set the pts for the output buffer
(and the duration, a.k.a. video_step, for video). Dispatch the decoded
data to the output and reset the internal buffer accumulation accounting.
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> void flush(video_decoder_t *this_gen);</PRE
></TD
></TR
></TABLE
>
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> void flush(audio_decoder_t *this_gen);</PRE
></TD
></TR
></TABLE
>
This function is called when either the xine engine flushes the stream, e.g.,
after a seek operation or when decoding runs too slow and frames arrive in
the output loops fast enough. Decoders should release everything they have
already decoded, drop the rest and wait for new input.
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> void reset(video_decoder_t *this_gen);</PRE
></TD
></TR
></TABLE
>
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> void reset(audio_decoder_t *this_gen);</PRE
></TD
></TR
></TABLE
>
This function is called when the xine engine resets the stream.
Decoders should get ready to receive data that has nothing to do
with the one it worked on up to now.
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> void discontinuity(video_decoder_t *this_gen);</PRE
></TD
></TR
></TABLE
>
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> void discontinuity(audio_decoder_t *this_gen);</PRE
></TD
></TR
></TABLE
>
This function is called when the xine engine encounters a pts
discontinuity. Decoders should forget all timestamping information
they might have accumulated from the stream to not confuse metronom.
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> void dispose(video_decoder_t *this_gen);</PRE
></TD
></TR
></TABLE
>
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> void dispose(audio_decoder_t *this_gen);</PRE
></TD
></TR
></TABLE
>
This function frees the resources used by the decoder plugin.
</P
></DIV
><DIV
CLASS="SECT2"
><HR><H3
CLASS="SECT2"
><A
NAME="AEN821"
></A
>SPU decoder</H3
><P
> A lot written above also applies for subpicture unit (SPU) decoders. The
SPU decoder API is declared in <TT
CLASS="FILENAME"
>src/xine-engine/spu_decoder.h</TT
>.
Details on the data, SPU decoders are expected to output, see the section on
<A
HREF="#OSD"
>overlays and OSD</A
>.
</P
><P
> However, there are some differences to consider. At first, unlike audio and
video, subtitles do not form a continuous stream. The decoder will therefore
only be called once in a while. The metronom call for timestamping,
which for audio and video is done by the engine, has to be done manually for SPU:
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> vpts = metronom->got_spu_packet(metronom, buf->pts);</PRE
></TD
></TR
></TABLE
>
</P
><P
> There are also two functions in the SPU decoder API, which have not been discussed above:
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> int get_interact_info(spu_decoder_t *this_gen, void *data);</PRE
></TD
></TR
></TABLE
>
Since SPUs are sometimes (on DVDs for example) used for user interaction like menu
highlights, this function can be called to get <TT
CLASS="VARNAME"
>data</TT
> filled with
the current interaction information. The caller and the decoder have to agree on
what this is exactly. With DVDs, you can get a copy of the current NAV packet here.
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> void set_button(spu_decoder_t *this_gen, int32_t button, int32_t mode);</PRE
></TD
></TR
></TABLE
>
Also for interaction, you can ask the decoder here to change the
current highlighting.
</P
></DIV
></DIV
></DIV
><DIV
CLASS="CHAPTER"
><HR><H1
><A
NAME="OUTPUT"
></A
>Chapter 6. xine's output layer</H1
><DIV
CLASS="SECT1"
><H2
CLASS="SECT1"
><A
NAME="AEN836"
></A
>Video output</H2
><P
> In order to allow for device-dependant acceleration features, xine
calls upon the video output plugin for more than just displaying
images. The tasks performed by the video plugins are:
<P
></P
><UL
><LI
><P
> Allocation of <SPAN
CLASS="TYPE"
>vo_frame_t</SPAN
> structures and their
subsequent destruction.
</P
></LI
><LI
><P
> Allocation of memory for use by one frame (this is to allow
for the ability of some video output plugins to map frames directly
into video-card memory hence removing the need for the frame to
be copied across the PCI/AGP bus at display time).
</P
></LI
><LI
><P
> Most important, the ability to render/copy a given
frame to the output device.
</P
></LI
><LI
><P
> Optionally the copying of the frame from a file dependant
colour-space and depth into the frame structure. This is to allow for
on-the fly colour-space conversion and scaling if required (e.g. the XShm
ouput plugin uses this mechanism).
</P
></LI
></UL
>
</P
><P
> Although these extra responsibilities add great complexity to your
plugin it should be noted that they allow plugins to take full advantage
of any special hardware-acceleration without sacrificing flexibility.
</P
><DIV
CLASS="SECT2"
><HR><H3
CLASS="SECT2"
><A
NAME="AEN850"
></A
>Writing a xine video out plugin</H3
><P
> The video out plugin API is declared in <TT
CLASS="FILENAME"
>src/xine-engine/video_out.h</TT
>
The plugin info of video out plugins contains the visual type, priority,
and the init_class function of the plugin.
</P
><P
> The <TT
CLASS="VARNAME"
>visual_type</TT
> field is used by xine to
determine if the GUI used by the client is supported by the plugin
(e.g. X11 output plugins require the GUI to be running under the
X Windowing system) and also to determine the type of information passed to the
<TT
CLASS="FUNCTION"
>open_plugin()</TT
> function as its <TT
CLASS="VARNAME"
>visual</TT
> parameter.
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> char *get_description(video_driver_class_t *this_gen);</PRE
></TD
></TR
></TABLE
>
This function returns a plaintext, one-line string describing the plugin.
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> char *get_identifier(video_driver_class_t *this_gen);</PRE
></TD
></TR
></TABLE
>
This function returns a shorter identifier describing the plugin.
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> void dispose(video_driver_class_t *this_gen);</PRE
></TD
></TR
></TABLE
>
This function frees the memory used by the video out plugin class object.
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> vo_driver_t *get_instance(video_driver_class_t *class_gen, const void *visual);</PRE
></TD
></TR
></TABLE
>
Returns an instance of the plugin.
The <TT
CLASS="VARNAME"
>visual</TT
> is a pointer to a visual-dependant
structure/variable. For example, if you had previously claimed your
plugin was of the VISUAL_TYPE_X11 type, this would be a pointer
to a <SPAN
CLASS="TYPE"
>x11_visual_t</SPAN
>, which amongst other things hold the
<SPAN
CLASS="TYPE"
>Display</SPAN
> variable associated with the
X-server xine should display to. See plugin source-code for other
VISUAL_TYPE_* constants and associated structures. Note that this
field is provided by the client application and so if you wish to add another visual
type you will either need to extend an existing client or write a new
one.
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> uint32_t get_capabilities(vo_driver_t *this_gen);</PRE
></TD
></TR
></TABLE
>
Returns a bit mask describing the output plugin's capabilities.
You may logically OR the <TT
CLASS="VARNAME"
>VO_CAP_*</TT
> constants together to get
a suitable bit-mask (via the '|' operator).
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> int get_property(vo_driver_t *self, int property);
int set_property(vo_driver_t *self, int property, int value);
void get_property_min_max(vo_driver_t *self, int property, int *min, int *max);</PRE
></TD
></TR
></TABLE
>
Handle the getting, setting of properties and define their bounds.
Valid property IDs can be found in the <TT
CLASS="FILENAME"
>video_out.h</TT
>
header file.
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> int gui_data_exchange(vo_driver_t *self, int data_type, void *data);</PRE
></TD
></TR
></TABLE
>
Accepts various forms of data from the UI (e.g. the mouse has moved or the
window has been hidden). Look at existing plugins for examples of data
exchanges from various UIs.
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> vo_frame_t *alloc_frame(vo_driver_t *self);</PRE
></TD
></TR
></TABLE
>
Returns a pointer to a xine video frame.
Typically the video plugin will add private fields to the end of the
<SPAN
CLASS="TYPE"
>vo_frame_t</SPAN
> structure which are used for internal purposes by the plugin.
</P
><P
> The function pointers within the frame structure provide a mechanism for the
driver to retain full control of how the frames are managed and rendered to. If
the VO_CAP_COPIES_IMAGE flag was set in the plugins capabilities then the
copy field is required and will be called sequentially for each 16-pixel high
strip in the image. The plugin may then decide, based on the frame's format, how
this is copied into the frame.
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> void update_frame_format(vo_driver_t *self, vo_frame_t *img, uint32_t width, uint32_t height, double ratio, int format, int flags);</PRE
></TD
></TR
></TABLE
>
This function will be called each time the colour-depth/space or size of a frame changes.
Typically this function would allocate sufficient memory for the frame, assign the pointers
to the individual planes of the frame to the <TT
CLASS="VARNAME"
>base</TT
> field of the
frame and perform any driver-specific changes.
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> void display_frame(vo_driver_t *self, vo_frame_t *vo_img);</PRE
></TD
></TR
></TABLE
>
Renders a given frame to the output device.
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> void overlay_begin(vo_driver_t *self, vo_frame_t *vo_img, int changed);
void overlay_blend(vo_driver_t *self, vo_frame_t *vo_img, vo_overlay_t *overlay);
void overlay_end(vo_driver_t *self, vo_frame_t *vo_img);</PRE
></TD
></TR
></TABLE
>
These are used to blend overlays on frames. <TT
CLASS="FUNCTION"
>overlay_begin()</TT
> is called,
when the overlay appears for the first time, <TT
CLASS="FUNCTION"
>overlay_blend()</TT
> is then
called for every subsequent frame and <TT
CLASS="FUNCTION"
>overlay_end()</TT
> is called, when
the overlay should disappear again.
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> int redraw_needed(vo_driver_t *self);</PRE
></TD
></TR
></TABLE
>
Queries the driver, if the current frame needs to be drawn again.
</P
><P
> <TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
> void dispose(vo_driver_t *self);</PRE
></TD
></TR
></TABLE
>
Releases all resources and frees the plugin.
</P
></DIV
></DIV
></DIV
></DIV
></BODY
></HTML
>
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