[Ffmpeg-devel] problems with av synchronization
Tue Oct 17 21:48:05 CEST 2006
I tried to use the map option, but it's not clear how it should be used
and I could never get it to work. I would prefer to not have to re-encode
the audio if I can avoid it. I do not understand why there should be any
synchronization problems, since the original mpeg and aiff files are in
perfect sync, as is the VOB file I created using mplex.
How should I go about using the map option? I have two streams, one for
audio and one for video.
On Tue, 17 Oct 2006, Michael Niedermayer wrote:
> On Tue, Oct 17, 2006 at 10:57:55AM -0700, Aaron Williams wrote:
> > I am trying to transcode a DVD VOB file into h.264 but am running into
> > problems where the audio seems to significantly lag the video, and the
> > lag seems to grow worse as the video progresses.
> > I am using the following command:
> > ffmpeg -i video.vob -f avi -y -croptop 32 -cropbottom 32 -vcodec h264
> > -acodec copy -b 1500k -bt 1000k -qmin 3 -qdiff 3 -bf 2 -croptop 60
> > -cropbottom 60 -b_qfactor 2 -pass 1 video.avi
> > Note that I have also tried with -async 1 but that made no difference.
> > I am just copying the original audio track, which is stereo AC3 at
> > 192kbps. The video is 720x480 NTSC at 29.97 fps.
> > Also of note that I got overflow errors if I did not specify -qmin 3.
> > This is with the latest SVN trunk version of ffmpeg compiled for an
> > Athlon64 on Linux.
> > I also had the same problem when I tried to use FFMPEG to merge a
> > separate aiff audio stream with the MPEG2 stream to create the vob. I
> > converted the aiff file to AC3 and used mplex to merge the files into an
> > initial VOB file which had perfect synchronization and used FFMPEG to
> > convert the vob to a compliant DVD VOB file using the copy codecs for
> > audio and video, again without any problems with the synchronization.
> > The problem seems to occur only when transcoding.
> > The cropping does not affect the synchronization problem.
> > Any suggestions would be appreciated. What little I could find on the
> > web regarding this did not seem to help.
> you can try to sync the video stream to the audio stream with -map ...
> alternatively reencode the audio and specify -async <something_larger_then_1>
> Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
> In the past you could go to a library and read, borrow or copy any book
> Today you'd get arrested for mere telling someone where the library is
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