[julie_m]

The problem is with ciné film shot at 24 frames per second being shown at 30 frames, or 60 fields per second. You need to show 4 frames of film over 10 fields of TV. So the pattern goes: Scan odd lines of film frame 1 -- Scan even lines of film frame 1 -- Advance film and scan odd lines of film frame 2 -- Scan even lines of film frame 2 -- Scan odd lines of film frame 2 again -- Advance film and scan even lines of film frame 3 -- Scan odd lines of frame 3 -- Advance film and scan even lines of frame 4 -- Scan odd lines of frame 4 -- Scan even lines of frame 4.

Reducing this to from 30 fps to 25 fps by interpolation can make the errors caused by the two-field, three-field cycle appear worse. It would be better to obtain the original four frames of 24 fps film from ten fields of 30 fps video and output them -- in the correct order; bearing in mind field 3e actually comes in before field 3o -- over eight fields of 25fps video, but I don't know of any software actually doing this. If I was really desperate, I'd have a play with the Source Code to ffmpeg and try to cobble something together.

(In countries using 25 frames per second for TV, ciné film is simply sped up from 24 fps to 25 fps for television. This is barely noticeable except for increasing the pitch of the music by almost a semitone.)