[MPlayer-users] how to "step backforward" ?

[Oliver Seitz]

> Hi dear all. I know there is a function to step forward by one single
> frame, by pressing
> . in mplayer. But I did not find the reverse function to step
> backforward. Is there
> this function in mplayer? Thank you.

No, it's not. It is not that easy. I'm not a developer, but my thoughts
about it are as follows:

Video files consist of intra-frames and inter-frames. Intra-frames contain
all the neccessary data for one single frame and can be decoded easily.
Inter-frames only contain the differences of the new frame in respect of
the frame that was just displayed last. So, if you're stepping back to an
intra-frame, you could do all the calculation backwards which looks like a
lot of code to be possibly written. Or you could search backwards to the
last intra-frame and do all the calculations as normal until you reach the
frame you desire. That looks like a lot of system load for a little
effect.

Then video files are usually designed to be read from start to end. There
are means implemented to help the player program always easily find the
start of the next frame in the stream. There is no help available within
the file to assist the player program finding the *previous* frame. That
might be another problem.

Those are some of the difficulties I suspect to arise.

But, that question is rising frequently these days. Perhaps some of the
developers will have a look at it...

Greets,
Kiste