How can you tell if the framerate in 25 fps video is resampled or sped up?

[xyzone]

I have some 25 fps videos from disc sources that I couldn't play on US players, and I am wondering if there is a way to tell if the fps has been resampled or if it's simply sped up 24>>25?

I can slow down a 25 fps video to play at 24 fps through controls in mpv to reduce the speed to 96%, but this only makes sense if the videos are sped up. And if videos are sped up, does it mean the sound is sped up to, or is it resampled to keep the same pitch?

I really hoped the NTSC/PAL issue would end with HD and that we would only have a universal 24 fps, at least for movies, but it looks like it's here to stay.

[LoRd_MuldeR]

Movies for cinema are almost always produced at 24 fps (HFR is still rare). So, if there is a 25 fps (PAL) version, it was created via speed-up. And if there is a 29.97 fps (NTSC) version, it was created via Telecine.

"Native" 25 fps footage exists too. But this kind of footage usually originates from TV productions. And it usually is interlaced.

For 25 fps footage that was created via speed-up from a 24 fps movie, the audio must be sped up too! That's because the sped up video is shorter than the original, so the audio must be shorter (faster) too, in order to keep the sync.

Resampling alone does not change the audio duration/speed, so that wouldn't work. However, often the audio is first sped up (e.g. the 48 KHz audio is sped up to 50 KHz) and then resampled back to 48.0 KHz or 44.1 KHz.

[xyzone]

Resampling alone does not change the audio duration/speed, so that wouldn't work.

Yes, I know, but I was talking about the pitch. If you resample the audio to fit the length but compensate to maintain the pitch, you will change the length but at least you won't warp the pitch. This can make a big difference with music.

However, often the audio is first sped up (e.g. the 48 KHz audio is sped up to 50 KHz) and then resampled back to 48.0 KHz or 44.1 KHz.

Sure, that goes without saying since optical media doesn't get published in 50KHz audio, but the pitch would still be screwed up, in that case.

[manolito]

And if videos are sped up, does it mean the sound is sped up to, or is it resampled to keep the same pitch?

In the old days the audio and the pitch were sped up, and most viewers (with the exception of some audiophiles) did not even notice. But for the last couple of years you do see more and more 24 -> 25 fps conversions where the pitch was corrected back to the original pitch.

But this is not a trivial task. Pitch correction can introduce terrible artifacts. Today Izotope Radius seems to have the best algorithm for pitch correction (it is also part of Adobe Audition). See this post:
http://forum.doom9.org/showthread.php?p=1732694#post1732694


Cheers
manolito

[xyzone]

I usually used 'Change Tempo' on audacity. I don't know how that stacks up against that proprietary algorithm but I never noticed any artifacts. The ideal situation would be to eliminate all NTSC/PAL framerates in 24 fps movie releases.