audio/Video framerate conversion

[hypercube]

can anybody explain to me why a 25fps movie soundtrack at 44100Hz
must be time stretched to fit in the same movie at 24fps ?

there is a similar stuff in BeSweet named "NTSC to PAL audio convertion".

in my mind, the movie duration is independent of video framerate.
and video framerate is independent of audio framerate. So what are
theses stuff ?

in my case, I record french version of totoro from Videotape: 25fps
I have also the japanese version from DVD: 24fps

[ChristianHJW]

The problems are if you decide to have a 25 fps movie play in 24 fps only, the duration will change than ( as its running slower ) and you have to stretch the audio to fit the new ( longer ) duration ...

[hypercube]

the duration will change
This is the problem for me.
let take a look on a movie, in a theater, I mean.
its framerate is at 24fps (near 24fps). Then this movie is
shown on european TV in PAL: 25fps.

1- the movie is simply played quicker.

or

2- the movie is converted in 25fps, with complex algorithm,
to reconstruct missing frames. => the movie duration is
preserved.

if the response is (1), I'm very surprised ! this is very dirty !
but it could explain definitively the need to time stretch audio track.

if the response is (2) algorithm is Telecine ?

[ChristianHJW]

1. is correct. You can simply check by comparing the duration of the same movie on a NTSC region 1 with a PAL region 2 DVD, 2nd will be shorter ....

[hypercube]

so, my totoro DivX at 23.976 fps, is produced by this scheme isn't it:

NTSC DVD 29.97 fps => inverse Telecine + desinterlace => 23.976 fps
progressive movie

reading http://www.labdv.com/leon-lab/video/interlace.htm,
I understand PAL movie is shorter than original Film.

But is NTSC movie shorter/longer than original Film ?

you said PAL is shorter than NTSC, so NTSC movie should have the
same size of Film, isn't it ?

I mean, Telecine conversion, preserve time duration, isn't it ?

In fact, NTSC is not very clear for me: Telecine algorithm
produce 30fps from 24fps. But NTSC is played at 29.97 fps
so, can we say that NTSC movie are played a little bit faster than
the required reading speed ? (I mean 30fps)

so to perform Inverse Telecine, it should be normal to force
input framerate to 30fps, not 29.97fps. And 23.976 movie should
not exists in this world. :p


can we resume the situation like this ?

- 24 fps : original movie
- 30 fps : Telecine convertion from 24 fps
- 29.97 fps: 30 fps movie played quicker to match NTSC standard
- 25 fps : 24 fps movie played quicker to match PAL standard
- 23.976 fps: does not exists, in fact this is an Inverse Telecined
30 fps movie. nothing else. so it's 24 fps.

[DIggedy]

*NTSC from a film source is 23.976fps with pulldown to make it 29.97fps (this does not change playback speed, it merely repeats frames. That is why people have observed things such as camera pans to appear jerkier on NTSC as opposed to PAL).

*NTSC from a video source is native 29.97 with no pulldown.

*PAL from a film source is 25fps, sped up from the original 24fps. This is termed 'PAL speed-up' by many people and is the centre of much debate.