[linux-dvb] Re: Audio sync

[Régis Bossut <rbossut@auchan.com>]

Klaus Schmidinger wrote:

>Are you saying VDR should set VPID, APID _and_ PCR-PID when recording?
>Would it then receive extra TS packets with the PCR-PID?
>What should it do with those? Would they have to be used when
>converting TS to PES in remux.c? What if PCR-PID == VPID?
>
>So far for channels where PCR-PID == VPID things appear to work fine.
>Since Oliver Endriss' driver fix live tv as well as replaying 
recordings work
>great. So apprently in case PCR-PID == VPID there's nothing else VDR
>would have to do, I guess.
>
>What's the reason to have an extra PCR-PID, anyway?
>
Background:

PCR means Program Clock Reference. Packets are sent at regular
intervals. Between packets, the clock is deduced from these timesyncs
packets from an internal PLL synchronized on them. This is one
mechanism. An other one is the DTS (decoding timestamp) which is carried
on audio and video packets in the MPEG headers. These DTS are generally
sent in the TS header of the packet starting the beginning of a frame
(this is the case for DVD MPEG streams, which do not contain a PCR).
However, some channels do not align beginning of frames at the start of
a TS packet and DTS is also not sent on every frame (I don't know how
the DTS is used in that case, the 13818 documents are quite diffficult
to understand...).

The question:
Which clock does the ARM use for audio/video synchronization ? I guess
it's DTS if present, PCR if not. But I'm not a guru...

/Régis




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