[MPlayer-users] converting 25 fps -> 23.976 fps?

[D Richard Felker III]

On Mon, Dec 15, 2003 at 01:50:05PM -0800, * wrote:
> [Automatic answer: RTFM (read DOCS, FAQ), also read DOCS/bugreports.html]
> Hello, I noticed that when I encode a vob stream at 25 fps
> to an avi at 23.976 fps (using -ofps 23.976) there are
> subtle jerks in action about every second.  I assume this is
> due to the way mencoder does the conversion (drops a frame
> occasionally as opposed to interpolating smoothly between
> frames)?
> 
> If this is true, is there any way to make it interpolate
> smoothly?

What would you have it do to "interpolate smoothly"?? This is a very
hard problem, and there's no way to do it correctly, since video is
grossly undersampled in the temporal direction.

For making this conversion, you should instead use -speed 24/25 (or
24000/25025 to be more precise) to slightly speed up both audio and
video. Keep in mind that you might have to resample audio too in order
to end up with an output rate that your codec will accept.

Actually, I just checked and -speed only works in mplayer, not
mencoder. If you _really_ need it, someone might be able to add it to
mencoder.

> Or is that not desirable for some other reason?

Unless you have a _VERY_ good reason, you should not be changing fps.

> Likewise, should I not try downconverting vobs at 29.976 fps
> to 23.976 fps?  Thanks!

VOBS at 29.976 fps don't exist (you mean 29.96 fps), and 29.97 fps is
rare since most vobs come from movies. If the movie is 29.97 fps,
chances are it's hard-telecined, and you need to apply inverse
telecine or it will look horrible. As a bonus, this will inherently
reduce the framerate to 23.976 fps.

BTW, why are you so interested in changing framerate?

Rich