[MPlayer-users] feature request

Rich Felker dalias at aerifal.cx
Thu Apr 28 02:59:23 CEST 2005

On Wed, Apr 27, 2005 at 05:25:49PM -0400, Robert Henney wrote:
> > On Wed, Apr 27, 2005 at 08:16:04PM +0200, Konrad Materka wrote:
> > > Dnia 27-04-2005, ?ro o godzinie 17:49 +0100, Johan van den Dorpe
> > > napisa?(a):
> > > 
> > > > What about being able to step backwards?
> > > 
> > > It was intended to be implemented in mplayey G2 (Generation 2), but last
> > > news about it was from July (August?) 2004. Long time ago. :-(
> > 
> > No it wasn't. This sort of feature is inherently not possible without
> > a huge seek-and-decode chain for each step. It will probably never be
> > implemented in any movie player simply because it doesn't belong. If
> > you need this function, decode all frames to jpeg files and look at
> > them with an image browser, or use a specialized nle program.
> cache thrashing and the unidirectional nature of the decoding are certain 
> to hinder any attempt to implement a feature such as this.

Huh? How is cache thrasing related??

> putting the cache thrashing aside for now, one way to lessen the seeking
> difficulty would be to keep a short history of the position of keyframes
> encountered while playing.  then the nearest keyframe previous to the frame

This is pointless. In any good format you can find the keyframes
easily without having to remember their positions.

> keyframe occurence is not exactly predictable and what constitutes a keyframe
> may not be clear from codec to codec.  another hurdle, and no good solutions
> I can think of for.

Nonsense; a keyframe is totally well-defined. Otherwise there'd be no
way to seek.

> one thing in our favor here is that no one expects seeking backwards to be
> the same as playing backwards.  even with terrible inefficiency and the poor 
> resulting performance of such a feature, something that would allow backing
> up by n frames would be thought of as invaluable by many.

Remembering locations won't help you do this. You actually have to
buffer all the frames. That's roughly 130 megs per gop.. :)

> getting the sound re-synced quickly after leaving the framesetting state is 
> another potential difficulty.  stepping forward right now does enough
> damage to the A/V sync, and stepping backwards can only be worse.

This is just because mplayer sucks. With a good player design (albeit
no good players exist) this is a non-issue.


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