[linux-dvb] PCM audio in MPEG2 stream

[as.schultz@t-online.de (Andreas Schultz)]

Hi developers,

I'm sorry, but i have to steal some of your time.

For the last month i have tried to construct an MPEG2 stream with LPCM 
audio in it, that willplay back correctly through the DVB card.

I can only make it *almost* work.

The source for the audio and video is a DVD. The DVD AC3 track is 
converted to LPCM and the reinserted in the MPEG2 video stream.
As long as i don't use PTS for the audio stream, everything is fine.

Trouble starts when i copy the PTS from the orignial AC3 frame into the 
LPCM frame. A single AC3 frames will expand to more than one LPCM audio 
frame and i can obviously use the PTS only for the first LPCM frame.

1. do i have to calculate and insert PTS for every LPCM audio frame i'm
    sending to the card?

What i'm currently seeing are variouse degress of picture and audio 
distortions depending on when i'm sending the frames. I order to narrow 
down the cause of the problem, could you please clarify the following 
points,

2. does audio/video syncing handled in the kernel driver or in the
    firmware?

3. How big are the video and audio buffers on the card (in bytes and/or
    in ms)

4. how (by what criteria) is audio and video synced at the moment?
    (could you provide some pseudo code on how it is done?)

5. what is the minimum required and maximum allowed latency for LPCM
    audio frames, so that the stream will stay in sync?

6. do the video and audio PTS need to match, i.e. should i align audio
    packets, so that their presentation time macthes at a video frame
    PTS?

Also, i would be extremly helpfull, if you could provide a sample 
MPEG2/LPCM stream with audio PTS that plays correctly. I appear to be 
unable to generate one myself.

Thanks a lot

     Andreas



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