29.97 -> 23.97, Why?

[lordbelial]

All of Doom9's guides strongly suggest performing IVTC to change 29.97fps to 23.97fps. I just have one question, why? I just keep it at 29.97 and Ive never had a problem. Does it save space? Increase quality? Just wondering. Thanks.

[Awatef]

Because there isn't much real 29,97fps video out there.
Most videos are telecined from the original 24fps to 29,97fps to be compatible with the NTSC standard.
So one uses IVTC (Inverse Telecine) to get the original 24fps (23,976fps) back and this has following advantadges:
1) smooth playback. if you keep 29,97fps, you'll have quite jerky playback (not that smooth because of repeated frames)
2) Much better quality by same bitrate

Of course you've got to keep the video in 29,97fps, if it's real 29,97fps, but that's rather rare: all movies and most anime are originally 24fps.

[jggimi]

Source that came from a 35mm film at 24fps will be Telecined to 29.97 for NTSC video broadcast or display.

Industry standard Telecined content will have interlace artifacts in 2 of every 5 frames, if kept at 29.97 and not run through some sort of Inverse Telecine (IVTC) process. See http://www.doom9.org/synch.htm for glorious detail.

Source that came from an NTSC video camera was never telecined, and should remain at 29.97. It may or may not be interlaced -- digital video cameras can often produce progressive frames. And, if you read through many threads here about anime, you'll discover that some animation -- usually the stuff destined for TV or video tape rather than theatrical release -- is shot with an NTSC video camera, and is also 29.97.

[Awatef]

@ jggimi
I would replace your "some" through "rare", since even if it's destinated for TV or video, 99% of Animes are 24fps (thanks god! there is some intelligent studios out there!)
Generally, studios making real 30fps movies or series are really idiots (do they think there is only NTSC system in this world?!), since such video can't be properly converted to PAL (which is being used in half of this world!). But 24fps is properly convertable to PAL (through speed up) or NTSC (through telecining), and can be then easily reverted to original 24fps.

[Tatjahna]

.. And to do a backup you need to put it back to 29.97fps in authoring dvd software !!! Is it me or there is "others" idiots ?

Any advice or explanations about why it's like that?

Ciao!

[Uli]

Originally posted by Tatjahna
.. And to do a backup you need to put it back to 29.97fps in authoring dvd software !!! Is it me or there is "others" idiots ?

Any advice or explanations about why it's like that?

Ciao!

It's in the specs. This is only setting a pulldown flag in the stream, that the DVD player telecines the stream on playback to 29.97 fps. The original coding is mostly FILM @ 23.976 fps. It's the same with SVCD btw.

greetz, Uli

[Tatjahna]

Thanx Uli..

You means that doing a pulldown isn't a kind of preset to reajust the framerate as I thought it was ?? With a pulldown, I don't really re-framerate my movie, but just set an information to make the movie compliant?

I have post a question about PAL to NTSC right after this topic..

To take my 25fps movie back to a "fake" 29.97, I need to put it to 23.97 right ? If so, how ? After, I can imagine that I will have to do a pulldown from 23.97 to 29.97..

And how to work with the audio and at what stretch settings ?

Any guide or help about that somewhere ?
Thanx in advance!

[Uli]

Originally posted by Tatjahna
...
You means that doing a pulldown isn't a kind of preset to reajust the framerate as I thought it was ?? With a pulldown, I don't really re-framerate my movie, but just set an information to make the movie compliant?
...

Yup, that's it excactly ;)

greetz, Uli

[jggimi]

See www.doom9.org/synch.htm

[Tatjahna]

Yeah I am currently reading it :)

A lot of technical terms and understanding, but I will surely got it :)

Thanx jggimi!