[vdr] FF card A/V sync suggestion

Udo Richter udo_richter at gmx.de
Mon Oct 23 15:07:29 CEST 2006


C.Y.M wrote:
> IRL, time is constant. But on playback if vdr doesn't clock its data, then
> desync is quite possible. For example, if there's nothing to "change" for a few
> video frames, because they're using "stack" compression they won't send an empty
> frame. So, consider this blackout time in "Lost". The theory is that problems
> are occurring because they're not sending empty null frames. Also, if they're
> clocking on video, not audio.

Out of curiosity, I've tried recording one of these flirt phone ad 
channels, that only send still pictures at extremely low data rates. 
Playback seemed to be fine more or less, though a/v sync is hard to 
notice there. The recording length and the video playback speed was more 
or less correct however.

Another hint: If frames are completely missing in the recording, they 
also don't account for VDR's absolute recording position and recording 
length. If there are enough of them, this should be noticeable.

> Does VDR store the pcr pid in the recordings? Is the pcr used
> during playback to clock the data?

Recordings are pure PES packet sequences of video and audio PES packets. 
PCR is not recorded. On playback, the PES packets are forwarded to the 
DVB driver without further modification. IMHO the playback sync only 
uses the PTS of the PES packets, however thats just guessing.

I'm not sure if the PES repacker does anything on recording or if PCR is 
used only on live. There are not much German channels with PCR on Astra 
anyway.

(look for VPID with nnn+nnn form in channels.conf)

Cheers,

Udo



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