[MEncoder-users] What's the special about the I-frames in libavcodec?

[Pepe]

El Martes, 31 de Octubre de 2006 19:52, Giacomo Comes escribió:
> On Tue, Oct 31, 2006 at 07:26:15PM +0100, Pepe wrote:
> > I have a dvd recorder Samsumg HR-725, with support for playing divx
> > videos.
> >
> > It plays well the videos I created with mencoder using xvid. It also
> > plays ok videos I downloaded from internet with DX50 fourcc (I think they
> > are divx).
> >
> > But if I use libavcodec then there's a strange effect: it seems the
> > I-frames are not displayed, so the image is merging with the previous
> > scene.
> >
> > I also use the program avidemux to edit videos. This program has a mode
> > call smart copy, it copies the original frames until it gets to a place I
> > edited then it regenerates there the frames until the next I-frame. If I
> > cut some frames right at the beginning of the video, obviously the first
> > frame it has to create is a I-frame. If I edit a xvid video, when I play
> > this edited video in the dvd recorder, the first frames (the ones created
> > by avidemux) have the same problem I mentioned above. When the second
> > I-frame is reached (an original one from xvid) the problem fixes and rest
> > of the video looks ok.
> >
> > I think avidemux uses ffmpeg for re-encoding the edited frames, and I
> > think ffmpeg is something related to libavcodec, isn't it?
> >
> > So I suppose there should be something special, something different in
> > the I-frames that libavcodec creates. Is there any way to create I-frames
> > more compatible with xvid or divx?
> >
> > Here is an example of a command line I use for libavcodec:
> >
> > mencoder -noodml -o test_av.avi \
> >   -oac copy \
> >   -ffourcc DX50 \
> >   -ovc lavc \
> >   -lavcopts
> > vcodec=mpeg4:vbitrate=1033:mbd=2:vstrict=1:vpass=1:turbo:vqmax=4:v4mv:tre
> >ll \ -vf-add scale=608:464 -zoom -sws 9 \
> >   -vf-add harddup \
> >   -force-avi-aspect 4:3 \
> >   video2.avi
> >
> > I tried several things. Setting fourcc to DIVX and XVID, use b-frames,
> > remove the vstrict option (which I need for another dvd player), or using
> > mpeg quantizers. No change at all.
> >
> > Any ideas?
>
> Try to use keyint with a lower value. May be the default (250) is too high
> for your player. The manual suggest <=132 for a strict MPEG-1/2/4
> compliance.

I've just tried with keyint=100 and then keyint=10. Nothing changed. The same 
result :-(

-- 
Pepe