[MEncoder-users] Re: framerate control question

[Trent Piepho]

On Tue, 21 Nov 2006, rob pfile wrote:
>
> when using decimate=2 or tinterlace,pullup to go from 60p->24p, i'd
> always see skipped frames and duplicated frames, which i interpreted
> as the filter not dropping enough or too many frames. but when i

I found that decimate=2 will not work correctly.  It helps to raise the hi
threshold setting, to something like say 1000, but it will still make
mistakes.

The problem is that the duplicate frames that were created for the 24 -> 60
conversion are not 100% identical.  There are encoding artifacts that make
them different.  In high motion scenes where there are lots of artifacts,
the duplicate frames will be rather different from one another.  On the
other hand, in low motion scenes the *non*-duplicate frames will be very
similar.

If you choose a low threshold for decimate, it will not drop frames in high
motion scenes that it should have dropped, resulting in very noticeable
stuttering.

In you choose a high threshold, it will drop frames that it shouldn't have
dropped in low motion scenes, resulting in a less noticeable stuttering.

I extracted frame difference information for some clips and analyzed it in
a statistics package.  There are no settings for decimate that will not
make a signficant number of mistakes.

That's what prompted me to come up with my own filter.  Just following a 3/2
pattern doesn't work when you have dropped frames from transmission errors or
commercials.