Tune decomb

[mc4_idea]

I have some very difficult source material I am working with. FPS are 29.97, but its source was film.

I used a standard telecide().

Then I try to apply decimate(cycle=5). It works when I try to use it on small samples of the file (say a minute or so). Now when I apply it to the whole file (about 35 minutes of footage) it starts throwing frames that obviously should not be thrown. The motion gets jerky. I here people talk about tuning decomb. How would I debug this problem myself?

Unrelated question:
If I convert to film, do I need to use progressive frame encoding with CCE?

[Guest]

Have you established BEYOND DOUBT that the source is not mixed film/nonfilm material? Clip out the part that you say is jerky and try that on its own. Is it still jerky?

There is one case I know of where Decimate can go wrong and I am working on a solution. If you have a segment that was animated at 12fps and then doubled to 24 and finally telecined to 30fps, you will get groups of 5 frames that have 3 duplicates, 2 of 1 frame and 1 of another. Decimate has no intelligence to remove one of the two duplicates of one frame, rather than the one duplicate of the other frame.

So, first check that you don't have hybrid film/nonfilm content, because decimating the nonfilm part will cause jerkiness, and second, check whether you have 12fps portions.

Another possibility is to try daxab's IVTC4, because its decimation is tied to the matching in such a way that the decimation can be more reliable. (The disadvantage is that you can't do the decimation standalone, or turn it on and off.) IVTC4 will fail on nonfilm portions too. With Decomb you can choose to render at 30fps using the Decimate(mode=1,threshold=50) functionality.

Please let me know what you find.