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</td><td valign="top" width="500"><font color="#ffcc00" face="arial, helvetica"><h2>DVB Demux API</h2></font>
<p>
The DVB demux device lets you set TS, PID and section filters in the DVB
device. This is internally accomplished through calls to the
<a href="demux_mod.xml">demux kernel module</a>.
The demux device can be accessed through /dev/ost/demux.
</p>
<p>
The function calls defined in the include file
<a href="dmx.h">dmx.h</a> are described in detail below:
</p>
<p>
<font face="arial, helvetica" size="+1">Demux API IO control calls</font>
<p>
<pre>
int open(const char *deviceName, int flags);
DESCRIPTION
This system call, used with a device name of /dev/ost/demuxn, where n
denotes the specific demux device to be opened, allocates a new filter
and returns a handle which can be used for subsequent control of that
filter. This call has to be made for each filter to be used, i.e. every
returned file descriptor is a reference to a single filter.
/dev/ost/dvrn is a logical device to be used for retrieving Transport
Streams for digital video recording. n identifies the physical demux
device that provides the actual DVR functionlaity. When reading from
this device a transport stream containing the packets from all PES
filters set in the corresponfing demux device (/dev/osst/demuxn) having the output set to DMX_OUT_TS_TAP. A recorded Transport Stream
is replayed by writing to this device.
This device can only be opened in read-write mode.
The significance of blocking or non-blocking mode is described in the
documentation for functions where there is a difference. It does not
affect the semantics of the open() call itself. A device opened in
blocking mode can later be put into non-blocking mode
(and vice versa) using the F_SETFL command of the fcntl system call.
PARAMETERS
const char *deviceName I Name of the demux device, which should be
/dev/ost/demuxn where n denotes the
specific demux device to be opened, or the
name of a logical DVR device, /dev/ost/dvrn.
int flags I A bit-wise OR of the following flags:
O_RDWR read/write access.
O_NONBLOCK open in non-blocking mode
(blocking mode is the default).
RETURNS
ENODEV Device driver not loaded/available.
EINVAL Invalid argument.
EMFILE "Too many open files", i.e. no more filters available.
ENOMEM The driver failed to allocate enough memory.
</pre>
</p>
<p>
<pre>
int close(int fd);
DESCRIPTION
This system call deactivates and deallocates a filter that was previously
allocated via the open() call.
PARAMETERS
int fd I File descriptor returned by a previous call to open().
RETURNS
EBADF fd is not a valid open file descriptor
</pre>
</p>
<p>
<pre>
size_t read(int fd, void *buf, size_t count);
DESCRIPTION
This system call returns filtered data, which might be section or PES
data. The filtered data is transferred from the driver's internal circular
buffer to buf. The maximum amount of data to be transferred is implied by
count.
When returning section data the driver always tries to return a complete
single section (even though buf would provide buffer space for more data).
If the size of the buffer is smaller than the section as much as possible
will be returned, and the remaining data will be provided in subsequent
calls.
The size of the internal buffer is 2 * 4096 bytes (the size of two maximum
sized sections) by default. The size of this buffer may be changed by
using the DMX_SET_BUFFER_SIZE function. If the buffer is not large enough,
or if the read operations are not performed fast enough, this may result
in a buffer overflow error. In this case EBUFFEROVERFLOW will be returned,
and the circular buffer will be emptied.
This call is blocking if there is no data to return, i.e. the process
will be put to sleep waiting for data, unless the O_NONBLOCK flag is
specified.
Note that in order to be able to read, the filtering process has to be
started by defining either a section or a PES filter by means of the
ioctl functions, and then starting the filtering process via the DMX_START
ioctl function or by setting the DMX_IMMEDIATE_START flag.
If the reading is done from a logical DVR demux device, the data will
constitute a Transport Stream including the packets from all PES filters
in the corresponding demux device /dev/ost/demuxn having the output set
to DMX_OUT_TS_TAP.
PARAMETERS
int fd I File descriptor returned by a previous call to open().
void *buf O Pointer to the buffer to be used for returned filtered data.
size_t count I Size of buf.
RETURNS
EWOULDBLOCK No data to return and O_NONBLOCK was specified.
EBADF fd is not a valid open file descriptor
ECRC Last section had a CRC error ­ no data
returned. The buffer is flushed.
EBUFFEROVERFLOW The filtered data was not read from the buffer in
due time, resulting in non-read data being lost.
The buffer is flushed.
ETIMEDOUT The section was not loaded within the stated
timeout period. See ioctl DMX_SET_FILTER for
how to set a timeout.
EFAULT The driver failed to write to the callers buffer
due to an invalid *buf pointer.
</pre>
</p>
<p>
<pre>
ssize_t write(int fd, const void *buf, size_t count);
DESCRIPTION
This system call is only provided by the logical device /dev/ost/dvrn,
where n identifies the physical demux device that provides the actual
DVR functionality. It is used for replay of a digitally recorded
Transport Stream. Matching filters have to be defined in the
corresponding physical demux device, /dev/ost/demuxn.
The amount of data to be transferred is implied by count.
PARAMETERS
int fd I File descriptor returned by a previous call to open().
void *buf I Pointer to the buffer containing the Transport Stream.
size_t count I Size of buf.
RETURNS
EWOULDBLOCK No data was written. This might happen if
O_NONBLOCK was specified and there is no more
buffer space available (if O_NONBLOCK is not
specified the function will block until buffer
space is available).
EBUSY This error code indicates that there are
conflicting requests. The corresponding demux
device is setup to receive data from the front-
end. Make sure that these filters are stopped
and that the filters with input set to DMX_IN_DVR
are started.
EBADF fd is not a valid open file descriptor
</pre>
</p>
<p>
<pre>
int ioctl( int fd, int request = DMX_START);
DESCRIPTION
This ioctl call is used to start the actual filtering operation
defined via the ioctl calls DMX_SET_FILTER or DMX_SET_PES_FILTER.
PARAMETERS
int fd I File descriptor returned by a previous call to open().
int request I Equals DMX_START for this command.
RETURNS
EBADF fd is not a valid file descriptor
EINVAL Invalid argument, i.e. no filtering parameters
provided via the DMX_SET_FILTER or
DMX_SET_PES_FILTER functions.
EBUSY This error code indicates that there are
conflicting requests. There are active filters
filtering data from another input source. Make
sure that these filters are stopped before starting
this filter.
</pre>
</p>
<p>
<pre>
int ioctl( int fd, int request = DMX_STOP);
DESCRIPTION
This ioctl call is used to stop the actual filtering operation defined
via the ioctl calls DMX_SET_FILTER or DMX_SET_PES_FILTER and started via
the DMX_START command.
PARAMETERS
int fd I File descriptor returned by a previous call to open().
int request I Equals DMX_STOP for this command.
RETURNS
EBADF fd is not a valid file descriptor
</pre>
</p>
<p>
<pre>
int ioctl( int fd, int request = DMX_SET_FILTER, struct dmxSctFilterParams *params);
DESCRIPTION
This ioctl call sets up a filter according to the filter and mask
parameters provided. A timeout may be defined stating number of seconds
to wait for a section to be loaded. A value of 0 means that no timeout
should be applied. Finally there is a flag field where it is possible to
state whether a section should be CRC-checked, whether the filter should
be a "one-shot" filter, i.e. if the filtering operation should be stopped
after the first section is received, and whether the filtering operation
should be started immediately (without waiting for a DMX_START ioctl call).
If a filter was previously set-up, this filter will be cancelled, and the
receive buffer will be flushed.
PARAMETERS
int fd I File descriptor returned by a previous call to open().
int request I Equals DMX_SET_FILTER for this command.
struct I Pointer to structure containing filter
dmxSctFilterParams parameters.
*params
RETURNS
EBADF fd is not a valid file descriptor
EINVAL Invalid argument.
</pre>
</p>
<p>
<pre>
int ioctl( int fd, int request = DMX_SET_PES_FILTER, struct dmxPesFilterParams *params);
DESCRIPTION
This ioctl call sets up a PES filter according to the parameters provided.
By a PES filter is meant a filter that is based just on the packet
identifier (PID), i.e. no PES header or payload filtering capability is
supported.
The transport stream destination for the filtered output may be set. Also
the PES type may be stated in order to be able to e.g. direct a video
stream directly to the video decoder. Finally there is a flag field where
it is possible to state whether the filtering operation should be started
immediately (without waiting for a DMX_START ioctl call).
If a filter was previously set-up, this filter will be cancelled, and the
receive buffer will be flushed.
PARAMETERS
int fd I File descriptor returned by a previous call to open().
int request I Equals DMX_SET_PES_FILTER for this command.
struct I Pointer to structure containing filter
dmxPesFilterParams parameters.
*params
RETURNS
EBADF fd is not a valid file descriptor
EINVAL Invalid argument.
EBUSY This error code indicates that there are
conflicting requests. There are active filters
filtering data from another input source. Make
sure that these filters are stopped before starting
this filter.
</pre>
</p>
<p>
<pre>
int ioctl( int fd, int request = DMX_SET_BUFFER_SIZE, unsigned long size);
DESCRIPTION
This ioctl call is used to set the size of the circular buffer used
for filtered data. The default size is two maximum sized sections, i.e.
if this function is not called a buffer size of 2 * 4096 bytes will be
used.
PARAMETERS
int fd I File descriptor returned by a previous call to open().
int request I Equals DMX_SET_BUFFER_SIZE for this command.
unsigned long size I Size of circular buffer.
RETURNS
EBADF fd is not a valid file descriptor.
ENOMEM The driver was not able to allocate a buffer of the requested size.
</pre>
</p>
<p>
<pre>
int ioctl( int fd, int request = DMX_GET_EVENT, struct dmxEvent *ev);
DESCRIPTION
This ioctl call returns an event if available. If an event is not
available, the behavior depends on whether the device is in blocking or
non-blocking mode. In the latter case, the call fails immediately with
errno set to EWOULDBLOCK. In the former case, the call blocks until an
event becomes available.
The standard Linux poll() and/or select() system calls can be used with
the device file descriptor to watch for new events. For select(), the
file descriptor should be included in the exceptfds argument, and for
poll(), POLLPRI should be specified as the wake-up condition.
Only the latest event for each filter is saved.
PARAMETERS
int fd I File descriptor returned by a previous call to open().
int request I Equals DMX_SET_BUFFER_SIZE for this command.
struct dmxEvent *ev O Pointer to the location where the event is to be stored.
RETURNS
EBADF fd is not a valid file descriptor.
EFAULT ev points to an invalid address.
EWOULDBLOCK There is no event pending, and the device is in non-blocking mode.
</pre>
</p>
</p>
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