[vlc-devel] Re: lip sych problem

[Derk-Jan Hartman]

On 28-nov-2005, at 0:14, Ross Finlayson wrote:
>> Should add here - RTP streams are actually 2 (at least) different  
>> streams
>> with different payloads
>
> This is correct.
>
>> that are not syncronised well (look at live555
>> mailing list). I.e - system will "sync on average bitrate", not on  
>> each
>> video packet. It means, that LiveMedia free library do not contain
>> mechanisms to make A/V sync/resync.
>
> But this is all completely false.  See <http://www.live555.com/ 
> liveMedia/faq.html#separate-rtp-streams>
>
> Once again: If your original data source (at the server end) has  
> (i) proper presentation times (corresponding to the 'wall clock'  
> time generated by calling "gettimeofday()"), and (ii) it properly  
> implements RTCP, then RTSP/RTP clients that use the "LIVE555  
> Streaming Media" software - including VLC - *will* get correct,  
> time-synchronized presentation times.
>
> If, however, your server does not implement RTCP, and/or does not  
> use properly synchronized presentation times to begin with, then  
> you're SOL.  End of story.
>
> I spent a lot of time making sure that the LIVE555 RTP/RTCP  
> implementation works properly - to generate correct, time- 
> synchronized presentation times at the client end.  I wish people  
> would stop claiming that this doesn't work.

The problem here is that there is tons of material in the wild that  
does NOT have proper timestamping and synchronisation. The fact that  
lots of this material works in most players, does not mean it is per  
definition streamable. The fact is the file is BROKEN. People need to  
understand this. For MPEG material, like 85% is probably broken.

DJ

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