[Live-devel] Synchronization drift

[Tony Kay]

The drift is noticable much more quickly than an hour...you can start to 
detect it within a few minutes. Is the audio frame duration extracted 
from the stream itself, or does it go on the bit rate estimation given 
in the test program???

- Tony

Ross Finlayson wrote:
> 
>> I am using testMPEG1or2AudioVideoStreamer to stream an MPEG2 file 
>> generated from a PVR-250. The streaming works fine, but the 
>> synchronization between audio and video drifts over time. The only 
>> references I have found for this are those that say it is the players 
>> fault. I have tried playing this stream on VLC/Mac and mplayer for 
>> linux. Both exhibit the problem (though mplayer _reports_ that the A-V 
>> is in sync).
>>
>> I know there are several timestamps going into this (RTP and 
>> presentation). Is it possible that the code has some sort of roundoff 
>> error or somthing that is causing the drift???
> 
> 
> Actually, yes, roundoff error is possible, because of the way that 
> presentation times for audio frames are currently calculated (in 
> "MPEG1or2AudioStreamFramer").  The audio presentation times are computed 
> by successive adding of the audio frame duration - but the audio frame 
> duration is precise only to 1 us resolution.  (Video, OTOH, isn't a 
> problem, because for video - unlike audio - the presentation time 
> information is present inside the MPEG video stream itself.)
> 
> How long does your stream play before you notice A/V getting out of 
> sync.  (The problem that I'm thinking of should not become noticeable 
> until at least an hour or so has elapsed.)
> 
> 
>     Ross Finlayson
>     LIVE.COM
>     <http://www.live.com/>
> 
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