[MEncoder-users] Mencoder does not cut exactly

[Etienne Buira]

On Thu, May 01, 2008 at 06:11:44PM +0200, belcampo wrote:
> BUIRA Etienne wrote:
> > On Wed, Apr 30, 2008 at 02:35:43PM +0200, TAJTHY Tammms wrote:
> >> Hi,
> >>
> >> I have a strange problem. I have a mjpeg avi file and I'd like to cut a part
> >> from it and convert to mpeg4. I detected the frames by VirtualDub. I did the
> >> following:
> >>
> >> mencoder ..compression-arguments.. -ss 1.120 -endpos 1:23:00.000 -o cut.avi
> >> patch.avi;
> >>
> >> My problem is that the resulted file does not contain the exact frames.
> >> Depending on the -ss option it can be +/-1 frames different. At the end
> >> position can be +/- 4 frames different. If I add 3-5 ms to the -ss and
> >> -endpos options so the start become puntual, but the problem still appears
> >> at the end.
> > 
> > Hi.
> > 
> > The -ss and -endpos method is quite inacurrate (even if you got a very
> > good accuracy for using those IMHO...).
> > 
> > You'd better use -hr-edl-seek, after selecting good timestamps using
> > -edlout. From the manpage: See http://www.mplayerhq.hu/DOCS/HTML/en/edl.html
> > for details.
> > 
> > (Sorry if this message appears twice, I messed up again with my email @)
> > _______________________________________________
> > MEncoder-users mailing list
> > MEncoder-users at mplayerhq.hu
> > https://lists.mplayerhq.hu/mailman/listinfo/mencoder-users
> video and audio are always off by ... msecs, sometimes earlier, 
> sometimes later, depending on source.
> If sound is off by say .4 sec. then 1 video frame will be added. So I 
> think that if you want to be frame-accurate, you'll need to decode video 
> and audio separate. You'll have to start at an I-frame till another 
> I-frame, not including it.

Doesn't -hr-edl-seek takes care of that, decoding the source file like
for playing it?

Anyway, I never experienced inacurracy nor A/V desynch since I use it
(but sometimes bigs ones using -ss/-endpos).