Strange problem with duplicate frame footage

Somebody has given me a ProRes movie file that runs at 30fps (not 29.98) and every fourth frame is a duplicate frame.

Is there a way of removing the duplicate frames and then doing a reverse telecine back to 23.976?

"Every fourth frame is a duplicate frame" means that the frames run A,B,C,C,D,E,F,F, ...

Then it is easy to remove the duplicate frames.
In Compressor Frame Controls: Rate Conversion to Fast (Nearest frame); Set Duration to 75% of source.
This gives you A,B,C,D,E,F, ...

If instead you have every fourth frame duplicated, like so: A,B,C,D,D,E,F,G,H,H,...
Then to remove the duplicate frames:
In Compressor Frame Controls: Rate Conversion to Fast (Nearest frame); Set Duration to 80% of source.
This gives you A,B,C,D,E,F,G,H, ...

It is only with interlaced material that "telecine" and "reverse telecine" make sense. If your movie is 60i, then what do you mean by "duplicate frames"? Set the FCP canvas to 100% and report exactly what you have.

Dennis Couzin
Berlin, Germany

the compressor speed change trick is tricky...
firstly, the pattern has to start on frame 1 otherwise it wont work,
plus in Compressor, i don't think you can preview an output like this satisfactorily.

the same trick could work in FCP where you'd have far greater control over it.

but yes, if it's interlaced footage, then it's a whole other ball game.


nick

I verified the Compressor method on a 15 second clip of form A,B,C,C,D,E,F,F, ...
I don't think Compressor will drift off track quickly because when I entered 75 for time percentage it entered 75.000 for me. Those three zeros are enough to keep in on track for 55 minutes. I believe Compressor's coding is generally more careful than FCP's.
When I tried entering 133.3333... for speed percentage in FCP it entered 133.33 for me.
Someone must do an experiment with a long clip to find out which application is sloppier in this case.

Dennis Couzin
Berlin, Germany