How to change fps for silent movies

[Enrik]

I have one mkv file with the same duration (the difference is 7 ms) as the m2ts file of the same silent film. However, the mkv frame rate is 19.980 and the m2ts frame rate is 23.976. How is this possible? Would it be possible to return the mkv to its original 23.976 fps without re-encoding?

MKV - 19.980 fps. Duration: 1 h 44 m 13 s 615 ms
M2TS - (original blu-ray) - 23.976 fps. Duration: 1h 44 m 13 s 622 ms

[jagabo]

Silent movies were shot at many different frame rates, usually less than 23.976. So 19.98 might be the correct rate. If so, the 23.976 fps video simply has duplicate frames to make up for the difference. Step through them frame by frame with an editor like VirtualDub2 and see.

[Enrik]

Silent movies were shot at many different frame rates, usually less than 23.976. So 19.98 might be the correct rate. If so, the 23.976 fps video simply has duplicate frames to make up for the difference. Step through them frame by frame with an editor like VirtualDub2 and see.

Therefore, I understand that the original ripper would have erased all duplicate frames and it's not possible to have 23.976 fps again.

Anyway, in case of frame deletion, shouldn't there be a greater difference between original and mkv in runtime?

[jagabo]

Silent movies were shot at many different frame rates, usually less than 23.976. So 19.98 might be the correct rate. If so, the 23.976 fps video simply has duplicate frames to make up for the difference. Step through them frame by frame with an editor like VirtualDub2 and see.

Therefore, I understand that the original ripper would have erased all duplicate frames and it's not possible to have 23.976 fps again.

Again? In the scenario I described there never was 23.976 fps. The 23.976 fps video was created from a 19.98 fps film by duplicating every 5th frame, not the other way around. But this is all speculation. You have to examine the videos closely to see exactly what's going on.

Anyway, in case of frame deletion, shouldn't there be a greater difference between original and mkv in runtime?

Frame rate change by duplicating or decimating frames doesn't change the frame rate. For example, if you start with exactly 1 second of 20 fps film (20 frames) and duplicate every 5th frame, those 20 frames becomes 24 frames. If you now display those 24 frames at 24 frames per second it still takes exactly 1 second to display them.

https://en.wikipedia.org/wiki/Frame_rate#Silent_films

The film may not really have been shot at 19.98 fps but may have been projected/digitized at 19.98 fps. That is something of a magic number for NTSC video. It allows each film frame to be displayed for three NTSC video fields, eliminating pulldown judder and jerkiness from frame duplication. Speeding up ~18 fps silent film to 20 fps is common because of this.

[Enrik]

Thank you very much, jagabo.