[FFmpeg-user] frame rate:24 or 24000/1001 for native movies

Discussion:

sean darcy

2018-10-31 22:27:13 UTC

I've got a bunch of soft-telecined dvds. I'm trying to get them back to
native format, 24fps.

ffmpeg -i input.vob -r [??????] output.mp4

All these vobs were originally theater movies, not TV productions.
Therefore I assume they were all shot at 24 fps, that is 24000/1000. But
all the examples I see have -r 24000/1001 , ~23.97. I can't imagine this
will make any visual difference but I'm puzzled.

These vobs were shot at 24 fps, so shouldn't inverse telecine be:

ffmpeg -i in.vob -r 24 out.mp4 ?

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Carl Eugen Hoyos

2018-10-31 23:56:09 UTC

Permalink

Post by sean darcy
I've got a bunch of soft-telecined dvds. I'm trying to get them
back to native format, 24fps.

Note that players should simply ignore the soft-telecine assuming
you are not using an old american tv set.

Post by sean darcy
ffmpeg -i input.vob -r [??????] output.mp4

The ntsc framerate is 30000/1001, if you divide this by the usual
telecine rate, you get 24000/1001. FFmpeg's console output will
tell you if it had to drop or duplicate frames. If - except maybe for
the absolute start of the video to correct different audio and video
start times - no frames are dropped or duplicated, the output frame
rate is correct.

Carl Eugen
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Phil Rhodes

2018-11-01 00:13:56 UTC

Permalink

Salient information:
It would be unusual for an NTSC-oriented DVD containing a feature film to have anything other than either 23.976 or 24fps material on it.
A vanishingly small minority of DVDs containing feature films, particularly early releases made from the same tape masters that had been prepared for VHS duplication, may have 3:2 pulldown on them and you should be able to use special measures to unwind this if it's been done competently.
Feature films are very commonly shot at 23.976 (strictly 24000/1001.) Theoretically, anything on an NTSC-oriented DVD will be shown at that rate.
P

From: Carl Eugen Hoyos <***@gmail.com>
To: FFmpeg user questions <ffmpeg-***@ffmpeg.org>
Sent: Wednesday, 31 October 2018, 23:56
Subject: Re: [FFmpeg-user] frame rate:24 or 24000/1001 for native movies

Post by sean darcy
I've got a bunch of soft-telecined dvds. I'm trying to get them
back to native format, 24fps.

Note that players should simply ignore the soft-telecine assuming
you are not using an old american tv set.

Post by sean darcy
ffmpeg -i input.vob -r [??????] output.mp4

Carl Eugen Hoyos

2018-11-01 00:38:10 UTC

Permalink

2018-11-01 1:13 GMT+01:00, Phil Rhodes

Post by Phil Rhodes
It would be unusual for an NTSC-oriented DVD containing a feature film to
have anything other than either 23.976 or 24fps material on it.

Carl Zwanzig

2018-11-01 04:24:16 UTC

Permalink

Post by Carl Eugen Hoyos
While - as so often - this is plain wrong depending on the definition
of "unusual" - the question was exactly if it is 24 or 24000/1001 (I
don't think 23.976 is likely).

If something was shot as a "film" it'll be 24.00000 FPS. As I understand,
it's common to assume 24000/1001 for North American market DVDs since the
player will up-sample to 30000/1001 for analog output and the actual
difference is invisible to humans.

z!
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Phil Rhodes

2018-11-01 10:35:46 UTC

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I'm not quite sure what you're describing as "plain wrong" but the facts are as follows:
- Feature films may be originated at either 24.00 or 23.976fps. Despite other comments in this thread it is common for features to be shot at the fractionally lower frame rate.
- Regardless of the origination rate, DVDs of feature films intended for traditionally-NTSC regions will be mastered in the expectation of 23.976fps playback. Force them to 24.00 and the sound will gradually go out of sync unless it's resampled.
Source: I have done this, for money, on feature films you can buy on DVD.
P

From: Carl Eugen Hoyos <***@gmail.com>
To: FFmpeg user questions <ffmpeg-***@ffmpeg.org>
Sent: Thursday, 1 November 2018, 0:38
Subject: Re: [FFmpeg-user] frame rate:24 or 24000/1001 for native movies

2018-11-01 1:13 GMT+01:00, Phil Rhodes

Post by Phil Rhodes
It would be unusual for an NTSC-oriented DVD containing a feature film to
have anything other than either 23.976 or 24fps material on it.

While - as so often - this is plain wrong depending on the definition
of "unusual" - the question was exactly if it is 24 or 24000/1001 (I
don't think 23.976 is likely).

Please remember that top-posting is still considered rude here, Carl Eugen
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Nicolas George

2018-11-01 10:25:51 UTC

Permalink

All these vobs were originally theater movies, not TV productions. Therefore
I assume they were all shot at 24 fps, that is 24000/1000. But all the
examples I see have -r 24000/1001 , ~23.97. I can't imagine this will make
any visual difference but I'm puzzled.

Maybe they were theater movies in the first place, but to get on DVD
they received conversion treatments, because the characteristics of DVD
media is not fully compatible with film.

The 24 â 24000/1001 conversion could have been done by dropping a few
frames or by slowing down the whole thing, with or without adjusting the
pitch of the audio.

Without exactly knowing what they were, you cannot revert these
treatments, and even knowing you probably could not.

Therefore, I think you would better encode the contents as it is on the
DVD and not worry about what it was originally.

In practice: don't specify the frame rate.

Regards,

--
Nicolas George