[MEncoder-users] Inverse telecine? framerate from 120000/1001 to 24000/1001

Rich Felker dalias at aerifal.cx
Thu Aug 31 03:07:48 CEST 2006

On Wed, Aug 30, 2006 at 08:33:15PM +0200, Munzuk wrote:
> > > In other hand, since someone said something about 'null frames', are
> > > those repeated frames null frames? if so, there must be a way to detect
> > > and remove it, isn't?
> >
> > They're not frames, they're just the absence of any frame at that
> > particular timer tick. "Removing" them would mean condensing all the
> > frames together without time between them so that the movie would play
> > 5 times too fast, which is surely not what you want.
> >
> > One other possible solution is initializing the encoder with a
> > framerate of 24 or 30 fps even though the container "framerate"
> > (actually timebase) is much higher.
> >
> > Rich
> >
> Yes, that's the idea, since these null frames, absence of frames, or whatever 
> they are, are so 'special', maybe is not too hard to develop a filter which 
> will be able to detect and remove them, then maybe would be possible to 
> convert the entire video to 24fps... or not... don't know, since the original 
> ripper took the decision of make it 120fps... it must be the best choice.
> sorry if I said too much nonsense :)

Yes, what you said is nonsense. The reason the file uses 120 tick/sec
timebase is that it's not all 24 fps but some 30 fps, and the smallest
common timebase that can represent timestamps correctly for both is
1/120 sec. If you try to make it 1/24 sec timebase, you will have to
discard one in every five frames from the 30 fps parts. If you want to
make it 1/30 sec timebase, you will have to show every 4th frame in
the 24 fps parts for double duration. Both choices will look very
ugly and choppy.


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