[MPlayer-users] A-V-sync in mencoder

[Ville Saari]

On Thu, Mar 18, 2004 at 05:07:51PM -0500, D Richard Felker III wrote:

> > And although the relation between
> > the input and output frames would then not be one-to-one, it would still
> > be predictable which would be quite an improvement over the current
> 
> No, it's entirely nonpredictable.

How come? If the input is constant framerate, the inverse telecine filter
uses constant input-output-ratio and the output is constant framerate, then
the only source of unpredictability is the phase of the telecine pattern,
which can cause a difference of one frame at most.

You might argue that a DVD is not a constant framerate source if it contains
mixed interlaced and telecined content, but if you define frame as two fields,
then it is strictly constant framerate. Unless it switches between PAL and
NTSC but I doubt that a DVD is allowed to do that in mid-title.

And if the inverse telecine filter doesn't use strictly constant
input-output-ratio, then it is plain wrong unless the video pipeline
after the filter can accept variable framerate. Which it of course can
not if it ends in an avi file.

> > And it most likely _will_ break it. In my experience -mc 0 almost
> > never produces acceptable results unless the input file was produced
> > by mencoder itself. And even then it wouldn't be 100% sure.
> 
> It does fine for DVDs, from my experience.

Try it for some DVD bonus features and be surprised. The DVD extras tend
to be encoded even less professionally than the main movie. The most
pathological case I've seen was some bonus feature on Disney's Pocahontas
DVD (PAL) which had sync-offset of several seconds from the start!

-- 
 Ville