lossless framerate change with ffmpeg?

[BabaG]

i haven't found, after a lot of searching, a simple way to change a 23.976fps mov file to a 24fps mov file using ffmpeg. i'm using linux and sometimes windows, btw. the -vf and -r options have been suggested but require a re-encode. i just want to copy the frames from the mov container (it's prores, btw) to a new container that plays at the new rate. i don't want to interpolate or drop frames, just play the same material faster. this used to be fast and easy with apple's cinema tools but those days are long gone.

the closest idea i've been able to come up with is to try to extract the raw or elementary material from the mov and then put it into a new mov container, defining that new container as 24fps in the process. would that work? what would that command look like?

thanks for any tips,
babag

[jagabo]

Someone else will probably give you a better answer. But I was able to remux to AVI at 24 fps, then back to MOV with:

ffmpeg -i input.mov -codec copy -r 24.00 temp.avi
ffmpeg -i temp.avi -codec copy new.mov

Audio sync was lost.

[BabaG]

thanks, jagabo.

from what i understand, the -r option causes a re-encode. also, the -copy option can't be used with a rate change. that's why i was wondering if i could just extract the mov contents, then re-wrap them into a new mov container that would be defined as having the new rate. same number of steps as you describe but , hopefully, no re-encoding.

thanks again,
babag

[Cornucopia]

Going from 23.976 to 24, you would expect to need to also change audio to avoid sync loss.

Some might slow down & resample, but most pro editing tools started with 24, pulled down to 23.976, TC'd to 29.97, edited, conformed, then IVTC'd back to 23.976, then pulled back up to 24.
With that in mind, audio should have been 48kHz sampling to start, pulled down to 47.952, edited, conformed, then pulled back up to 48. So if the audio is 47.952, you know what to do. If it's 48, you could raise it to 48.048kHz.
Similar things would happen with 44.1kHz audio, though that would not have been the choice of a (good) pro sound engineer.

I thought that was a pretty good answer, @jagabo, but maybe not. A rate change of this sort is really just a metadata change.

Scott

[gdgsdg123]

...I was able to remux to AVI at 24 fps, then back to MOV with:

ffmpeg -i input.mov -codec copy -r 24.00 temp.avi
ffmpeg -i temp.avi -codec copy new.mov

This hack seems to be working for minor FPS changes... Just verified with a "29.97 to 30" test.

[BabaG]

thanks gdgsdg123 and all. i'd be curious how the hack works on a long file, like a couple of hours. any verification for that? it keeps the same number of frames, unaltered?

thanks again,
babag

[gdgsdg123]

i'd be curious how the hack works on a long file, like a couple of hours. any verification for that? it keeps the same number of frames, unaltered?

Very likely.

Related: https://forum.videohelp.com/threads/379834#post2570613

[blud7]

It works even if you use mkv container instead of avi.
And I can verify it works on a 2 hr plus file.
Had a few videos encoded with Handbrake with pseudo vfr, even though mediainfo reported cfr.