NTSC/PAL but exact film length: How so?

[Anonymous5394]

A friend of mine showed me two avi's of 90 mins length of exact same feature but encoded in PAL and NTSC frame rates. How is this possible? Incredible really. There were no audio synch issues and everything played perfectly.

I assumed that the PAL one would be considerably shorter due to time differences. The audio was exactly the same in both. Is it something to do with squeezing an extra framerate/per second in at PAL speed that keeps the film length? I heard compressing audio is another method to do this thing. For techno minded to explain I think. Thanks guys!

[lordsmurf]

fps does not equal length.
Yes, you can insert dupe frames, to adjust for 24p film to 25p PAL video.

The other method is using the frames, frame-to-frame, from 24 to 25fps. This makes each second 1 frame shorter, or about 4% -- and yes, audio will lose sync. The fix for this is to shrink audio, but that will "chipmunk" it. To fix this, you attenuate pitch by ~4%, and problem solved.

This is only a real fix for progressive film.

With interlaced video, it gets very complicated.

[Anonymous5394]

Complicated, you are not kidding! I always assumed if you change from NTSC to PAL or reverse that 4% time difference would occur in every case. Thanks for info.