[MPlayer-dev-eng] mencoder start position

[D Richard Felker III]

On Sat, Dec 04, 2004 at 12:53:11PM +0100, Jérôme Petazzoni wrote:
> 
> 
> >When I encode normal avi file then -ss option work correct (when I
> >choose 51,27 then encoding start from that position) but I've got a few
> >files in matroska and I want to cut them. To check start position in
> >frames I must extract video track (mplayer doesn't show actual frame in
> >matroska - only decoded frames). When I've got video track extracted
> >from mkv mplayer and mencoder  as start position choose next keyframe
> >from choosen position.
> 
> I seem to have the same problem with MPEG2 and MPEG4 streams. When I try 
> to extract some specific frames (with "mplayer -ss", not "mencoder -ss" 
> so I don't know if it's the same mechanism behind it ...) I observe some 
> serious discrepancies between the frames extracted (I have the very same 
> video sequence in VOB format, in MPEG4 ISO (quicktime) format, and a few 
> others ; and when trying to get some specific frames, I end up with 
> slights offsets - because indeed "mplayer -ss" doesn't do accurate seeking).
> 
> It seems that no mplayer guru wants this feature, so we will probably 
> end up coding it ourselves :-)

For mpeg1/2 it's a totally different problem. The format sucks really
bad, so it's impossible to do accurate seeking without being VERY SLOW
(i.e. reading the whole file). For other file types the problem is
mainly that you can only seek to keyframes.

Rich