my 2¢

1 files changed, 26 insertions, 9 deletions

diff --git a/dvb-spec/HOWTO-use-the-demux-api b/dvb-spec/HOWTO-use-the-demux-api
index 2f1fe8c3d..ee782db6d 100644
--- a/dvb-spec/HOWTO-use-the-demux-api
+++ b/dvb-spec/HOWTO-use-the-demux-api
@@ -3,10 +3,12 @@
 
 What has changed since the old Nokia OST API?
 
-  file naming:
+  device node naming:
     - /dev/ost directory is now called /dev/dvb
     - each DVB adapter has it's own directory /dev/dvb/adapterX
-    - here you'll find a number of frontend devices /dev/dvb/adapterX/dmxY
+    - the devfs devices names are identical to those
+      creatd by the makedev.napi script on non-devfs systems
+    - here you'll find a number of demux devices /dev/dvb/adapterX/dmxY
     - driver header directory is located now in /usr/include/linux/dvb/
     - we have a linux/dvb/version.h file, this is included by all headers which
        don't use the original OST API anymore
@@ -45,7 +47,7 @@ What is a demultiplexer?
 I have set up the frontend and now I want to see some video!
 What do I have to do?
 
-  When you have an MPEG video decoder on board we can set up the demultiplexer 
+  When you have an MPEG video decoder on board you can set up the demultiplexer 
   to feed the related PES packets into the MPEG decoder:
 
 	#include <linux/dvb/dmx.h>
@@ -69,15 +71,20 @@ What do I have to do?
 	}
 
   This will unpack the payload from all transport stream packets with 
-  payload ID <pid> and feed it into the MPEG decoder. When pes_type is set
+  packet ID <pid> and feed it into the MPEG decoder. When pes_type is set
   to DMX_PES_VIDEO it will be handled as video data. Other types are
   DMX_PES_AUDIO, DMX_PES_TELETEXT, DMX_PES_SUBTITLE which will be fed into 
-  the corresponding decoders. 
+  the corresponding decoders (if these deocders exist in hardware or firmware).
+  DMX_PES_TELETEXT usually means VBI insertion by the PAL/NTSC encoder for display
+  on a connected TV set. If you want to avoid sending the data to one of the
+  decoders, use pes_type = DMX_PES_OTHER.
 
-  Open such a PES filter for each substream you want to decode.
+  You must open the demux device once for each PES filter you want to set.
+  E.g. if you want audio and video, you must have two distinct file descriptors
+  for the two filters.
 
   DMX_PES_PCR is used by the decoder to achieve a correct timing syncronisation
-  for the partial audio/video/... substreams.
+  between the audio/video/... substreams.
 
   Note that you have to keep the frontend and demux filedescriptor open until
   you are not interested in the stream anymore. Old API versions did not shut
@@ -90,10 +97,17 @@ I want to record a stream to disk! How?
 
   Set up a filter for each substream you want to record as above but set 
   the pesfilter.output field to DMX_OUT_TAP. Then you can use read() calls 
-  to receive the PES packets.
+  to receive PES data.
 
   When you want to receive transport stream packets use DMX_OUT_TS_TAP and
-  read the stream from /dev/dvb/adapter0/dvr0.
+  read the stream from /dev/dvb/adapterX/dvrY. The dvr device gives you
+  a multiplex of all filtered PES data with DMX_OUT_TS_TAP. E.g. if you
+  want to record video and audio, open demuxX twice and set two PEs filters
+  with DMX_OUT_TS_TAP, and open dvrX once to read the TS.
+
+  [ The current API does not allow you to specify you an input/output
+    routing for section filters. So you can't get multiplexed section
+    data from the dvr device. ]
 
   Don't forget to keep all device filedescriptors you use open.
 
@@ -177,6 +191,9 @@ How to do table id filtering?
 
   Then submit the DMX_SET_FILTER ioctl.
 
+  The filter comprises 16 bytes covering byte 0 and byte 3..17 in a section,
+  thus excluding bytes 1 and 2 (the length field of a section).
+
 -------------------------------------------------------------------------------
 
 What are not-equal filters?