[MEncoder-users] M4V to WMV out of sync

[Wietze]

Bill Crockett writes:
> Wietze <wietzuh <at> gmail.com> writes:
>
> > Hi Everyone, When transcode a M4V video file to a WMV, the resulting 
> > WMV is out-of-sync. The audio gradually going out of sync with the 
> > video. I'm only having this problem with M4V files.
> >
> > I'm using the following mencoder command: "input.mp4" -of lavf 
> > -lavfopts format=asf -vf harddup -ovc lavc -oac lavc -lavcopts
> > acodec=wmav2:vcodec=wmv2:autoaspect:keyint=25:vqscale=2  /
> > :vqmin=2:aglobal=1:vglobal=1  -mc 0 -ofps 25 -o "output.wmv"
> >
> > While transcoding, I get the following warning several times: [wmv2 @ 
> > 012521a0]warning, clipping 1 dct coefficients to -255..255
>
> For dct coefficients, try increasing the "vqscale" range.  I had this
problem and had to use vqscale=5  to stop the clipping.  However this was
encoding from FLV to AVI.
>
> For audio sync, try adding -demuxer lavf at the beginning.  Try it without
-mc 0 and if no improvement try it with -noskip -mc 0.  I don't know why,
but the -demuxer lavf had the audio and video back exactly in sync for
videos I had problems with.
>
> Bill

The dct coefficients problem was solved by vqscale=5, thanks for that.
However, the sync problem still isn't solved. It seems -demuxer lavf doesn't
change anything. Transcoding without -mc 0 seems to reduce the problem, but
the sync problem is still noticeable. 
What I really don't understand is why this AV sync problem only occurs while
transcoding M4V to WMV, since I don't get this problem with transcoding M4V
to AVI/MPEG4/FLV/DIVX. MPEG4/FLV to WMV also transcodes correctly. 

Wietze