Framerate conversion Q: PAL to NTSC to NTSC

[DoctorM]

I'm trying to figure the correct script for an odd pattern.

The source is NTSC but it was created from a PAL master by duplication of frames.

That is, 5 unique frames followed by one duplicate (all progressive). (ABCDEE)

At first I was going to use fdecimate(rate=25).assumefps(23.976) and then slow the audio accordingly.

But that doesn't seem right since the pattern suggests 29.97 * (5/6) which would make it 24.975.

I guess the question is do I decimate to 25 or 24.975.
If I use 24.975, a standard slowdown on the audio track probably wouldn't sync, whereas a decimation of 25 might still leave some duplicate frames.

I'm leaning towards doing something strange like:
assumefps(30).fdecimate(rate=25).assumefps(23.976)

Any thoughts?

[Sagekilla]

It sounds like what happened was, for every 5 frames the 5th was duplicated (25 fps ABCDE --> 30 fps ABCDEE), then they slowed down the video to 29.97 fps to get NTSC video. That's why if you do 29.97 * 5 / 6 you get 24.975 -- It's not "true" 29.97, it's really 30 fps played at 29.97 fps.

[DoctorM]

Which would make assumefps(30).fdecimate(rate=25).assumefps(23.976) the best way to repair it.

I'd leave it alone but I hate speed up and the jitter from the dupe frame makes me crazy.

[Sagekilla]

Yes, that sounds like that'd do the trick. I'm not a complete expert when it comes to this kind of trickery but that sounds like what happened.

[DoctorM]

Thinking about it some more, that method would again make 25 -> 23.976 audio conversion desync (and vice versa).

So I did the math --
23.976 -Speedup-> 25 (30) -slowdown by 1.001001-> 24.975 (29.97)

And there's 24.975 again.
If they really did 23.976 to 24.975 (which would be a pain to calculate an audio correction for), but maybe it's non-drop frame (or is it drop frame?).

I never got my head around that, but IIRC it is possible to use true 30fps video on a DVD.

[neuron2]

Post a link to a decent sized piece of the NTSC source VOB. Then we can tell what was done.

[DoctorM]

Ok http://rapidshare.com/files/152574185/Clip.mpv.html (77.9mb)

[manono]

Rapidshare seems to be having problems at the moment and I can't get the video.

If it's really as you say (5 unique frames followed by one duplicate (all progressive). (ABCDEE)), then a simple:

Decimate(6)
AssumeFPS(23.976)

will return it to progressive 24.975fps with the dupe frames removed, followed by slowing it to 23.976fps. As for the audio, in BeSweet you can set "Change Framerate from 24.975 To 23.976". I do this all the time and first convert the original DVD AC3 audio to PCM WAV before then converting the WAV file back to AC3 using something else.
I guess the question is do I decimate to 25 or 24.975.

Unless you want a dupe frame every 40 seconds or so, you want 24.975fps.

Again, this assumes what you said the source is like is correct.

[DoctorM]

Sorry about RapidShare. Hopefully they'll sort it out. I was originally going to use Mediafire.

Unfortunately, you'd pretty much have to go through 1000 frames to find out if they tossed an extra one in.
I didn't know if there was a standard way this was normally done.
Is it really likely the film was sped up to 25 fps for the master, and then it was slowed down again to 24.975 before duplicate frames were generated? That's got to be a disaster for the audio track.

As far as 24.975 to 23.976 audio conversion, you're talking either CLI, or worse still, BeSweet GUI (the wizard doesn't allow custom frame rate changes).

I suppose it is the best answer though since I can't figure how else you'd create something like this, let alone repair it correctly.

[manono]

Yeah, MediaFire is much better, in my opinion. And you don't have to wait. I finally got the clip on my 4th try. We didn't really need 81 seconds when 10 seconds would have been plenty to see what was going on. And you were correct about there being a dupe every 6th frame.

It's all about the drop frame.

30fps is to 29.97fps as
24fps is to 23.976fps as
25fps is to 24.975fps.

The standard way to convert a PAL source to NTSC is to slow both the audio and video to 23.976fps. Another way is to use the PAL master for the NTSC DVD and field-blend the heck out of it, perhaps the most common way. Another way is what you have, just add a dupe frame after every 5th frame. And another and better way is to add an additional frame after every 5th frame, but to add it in the form of a field every 10 fields. It makes for a smoother playing video.
As far as 24.975 to 23.976 audio conversion, you're talking either CLI, or worse still, BeSweet GUI
Worse still? If you want to slow the audio, it's what I always use and it does a good job. I suppose you can use some WAV Editor, if you prefer.

They used the PAL master from some crummy PAL version of the film. Better would be to wait for the real NTSC version of the film on DVD, one put out by Paramount sometime. The African Queen is, I believe, the only IMDB Top 250 film without a decent NTSC DVD yet. Which version is this, the Korean NTSC DVD of the film?

[DoctorM]

If it's the drop frame that gives us this rate, does that mean it was really slowed from 25 to 24.975 or was it flagged as such for playback. (Like I said I've always been unclear how df and ndf work).

And yup, AFAIK the Korean DVD is the only commercial NTSC release of the film in existence... and as it turns out it's from a PAL master (which would have made converting it from a PAL DVD a better idea, but it's what I have).

It's also the only AFI top 100 not on DVD. While I have no evidence of it, I believe the master has been damaged or lost and the studio is embarrassed to admit it.
There is no other good reason for this not to exist on DVD in the U.S.

Thanks for the info.

[manono]

If it's the drop frame that gives us this rate, does that mean it was really slowed from 25 to 24.975 or was it flagged as such for playback.
I don't know and it doesn't matter. In this case it's probably flagged as such since they used a 25fps master as a source, but you still treat it as 24.975fps for the dupe removal.

[DoctorM]

Good deal. Thanks I'll give it a go.

[DoctorM]

Seems to work just fine.

I am always overwhelmed by the irony that BeSweet's command line is easier to use than BeSweet GUI.
I would have used BeLight but for some reason it claims for SoundTouch "Convert frame rate without changing pitch". I think that's just a flawed description though, since it generates the same -ota command.

Edit: I was unfamiliar with Mode 6 in decimate so I read up on it. I didn't realize it was complete blind removal of dupes below threshold.

All things considered fdecimate(24.975) is probably the better answer. It will at least intelligently attempt to reach the desired framerate without cutting too many if the motion is too low or leaving too many if there are compression artifacts or other flaws.

About the same result but I think the audio sync is a bit better.