[MPlayer-users] Re: [MEncoder] Synchonization lost when using Vorbis in a OGM

[D Richard Felker III]

On Tue, Jun 17, 2003 at 07:23:12PM -0500, Jonathan Rogers wrote:
> [Automatic answer: RTFM (read DOCS, FAQ), also read DOCS/bugreports.html]
> Rodolfo J. Quesada wrote:
> >[Automatic answer: RTFM (read DOCS, FAQ), also read DOCS/bugreports.html]
> >Hi,
> >
> >This is my first post to this list... As I had been looking for a long 
> >time how to deal with a problem I got recently...
> >
> >I'm trying to compress some VOBs copied with vobcopy, and after that, 
> >dump the audio, convert it to Vorbis, and mux it all, with ogmmerge to 
> >get a nice OGM.
> >
> >The problem is, that those VOBs after starting mencoder, keeps saying 
> >that there was duplicate frames, enters and leaves telecine mode, it 
> >jumps from 23.976 to 29.970 in those changes... All of that things are 
> >expected by the nature of the DVD, when I got to the final AVI, with an 
> >AC3 audio track (-oac copy), the A-V sync is always around 0.000, with a 
> >few tens of milliseconds changes... That's still fine...
> >
> >Then I dump the PCM audio...
> >
> >cat *.VOB | mplayer -vc null -vo null -ao pcm -aofile audio.wav
> >
> >And I get a pretty big PCM file... Then I encode it...
> >
> >oggenc -q0 audio.wav
> >
> >And got an audio.ogg file...
> >
> >Then, I merge it...
> >
> >ogmmerge -A video.avi audio.ogg -o pelicula.ogm
> >
> >And when I play it with MPlayer, the sync ratio jumps up to 15 seconds, 
> >in some scenes where the telecine mode was enabled... It gets 
> >desynchronized all the way, in the plain old 29.970fps scenes, the audio 
> >is synced, but not in the 23.976 ones... I tried it in Windows Media 
> >Player 6.4, and those scenes not synchonized get blurred or stoped, and 
> >follows the audio synchronizations nicely, but the video quality is not 
> >appealing at all... Pretty ugly in fact...
> >
> >So, the question, somebody has faced this problem before? It can be 
> >solved?... I really love OGM... The audio is so sweet, even at a -q0 
> >ratio...
> 
> I have a very similar problem. I transcoded a movie from DVD to MPEG-4 
> which has many cuts between NTSC interlaced video at 29.97 and telecined 
> film at 23.976. Since there is 29.97 fps video in there, I encoded to 
> 29.97 and used pp=lb.
> 
> When I play the AVI containing the encoded video and PCM audio with 
> mplayer, the sync is good. However, when I play the OGM produced with 
> the Vorbis audio and ogmmerge, the sync is horrible. The A-V delta gets 
> up to a second or two by mplayer's admission and according to my eyes 
> and ears.
> 
> In particular, mplayer starts getting out of sync when the movie cuts to 
> an originally telecined segment. It somewhat regains sync when the movie 
> cuts back to something that was originally NTSC. During film segments, 
> mplayer's "A-V" value will sometimes jump from less than one second to 
> greater than one. If I seek forward, then back to the same spot, sync is 
> usually restored.
> 
> Now, it's time for the kicker. When I play the exact same OGM with Xine, 
> there are no sync problems. Based on my previous experience with 
> mplayer's flakiness in seeking and sync of OGM movies and this mess, I 
> tend to think this is a bug in mplayer. It could be a bug in ogmmerge, 
> but if so, Xine is somehow working around it.

Well OGM is not standard by any means, it's a hack from OggDS. And
since WMP also fails to play the file (using OggDS), I don't think we
can really call this a bug in mplayer -- it's mimicing what OggDS
does. :))

My guess is that ogmmerge outputs something bogus when it gets a
0-length frame from the avi file. Probably a 0-length ogg packet. A
better approach, since ogm has timestamps, would be to just omit
output on 0-length input frames...

Rich