[linux-dvb] Re: Question about audio/video synchronization (was : [vdr] Lip-Synchronisation)

[Ralph Metzler <rjkm@metzlerbros.de>]

Johannes Stezenbach writes:
 > On Thu, Feb 13, 2003 at 03:53:29PM +0100, Régis Bossut wrote:
 > >
 > > This question, asked yesterday, got no answer. It is mainly directed to 
 > > the firmware developpers :
 > > 
 > > >Would it be possible to know how does the firmware synchronize audio 
 > > >and video (PTS ?, DTS ?, other ?)
 > > >1) during reception
 > > >2) during playback
 > > >and what is the maximum time distance between audio and video after 
 > > >which audio or video is not output
 > > >1) during reception
 > > >2) during playback
 > 
 > I don't really know all the details because synchronization
 > is handled in TI's (binary only) RTSL. Synchronization is always to
 > the PTS, if the MPEG decoder uses DTS internally is unknown to me. The

The DTS is not used. The decoder only gets the elementary video stream and
the PTSs in a separate buffer.
Synchronization can basically only be switched on or off and is, AFAIK, handled
directly by the decoder microcode (not even the firmware or RTSL). This 
runs on an unknown DSP (maybe compatible in code to some other TI DSP?).


 > limits for synchronization are set by the available decoder
 > buffer space, so depends on bitrate etc.
 > 
 > > >This would help us [me] to understand why the sound is sometimes 
 > > >missing during reception and how to feed better the audio and video 
 > > >data during the playback.
 >
 > I have no sound problems in reception, and playback
 > works reliable with VDR and ntuxplayer, provided the recorded
 > streams are OK.

I also have no problems with missing sound. On which channels can you
observe this?
There are sometimes problems with synchronization with low-bitrate
MPEG1 files. This could be caused by PTS buffer overflows but I did 
not investigate this further.


Ralph



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