29.97fps->24fps with decomb3.x for capture video possible?

[wing1]

Can this filter be used to convert 29.97fps capture clip to 24fps film? If it can be done, what decimation setting should be used to perform such task?

[Guest]

If your captured video is 3:2 pulldown telecined progressive source, e.g., from film content, then yes. Your script could be as simple as this:

Telecide()
Decimate(cycle=5) # or even just Decimate()

[whosithis]

What if the source is NTSC 29.97 fps interlaced material? Is it possible to construct a 24 fps film progressive video stream from regular NTSC video?

[Guest]

Strictly speaking, a "progressive frame" is one composed of two fields sampled at the same moment in time. Interlaced video has fields all shot at different times (1/50 or 1/60th second apart). So strictly speaking the answer is no.

If we relax our definition of progressive to mean a frame without interlacing artifacts then you can consider that frames passed through FieldDeinterlace are converted to progressive frames. By then applying Decimate(cycle=5) you can reduce the frame rate. It will look a bit jerky, however, during fast pans and movements. The problem is that taking 30fps interlaced to 24fps by decimation will inevitably leave temporal gaps. You could instead convert by using frame blending after the FieldDeinterlace. I believe there is a filter available for doing that (ChangeFPS?), but Decomb won't do it.

In summary, you could try:

FieldDeinterlace(full=true)
Decimate(cycle=5)

or:

FieldDeinterlace(full=true)
ChangeFPS(???)