Removing baked-in PAL speed-up from an NTSC source

[jerrycan]

Hi. I apologize if this question has been asked many times before. Loads of searching turned up nothing solid.

Anyway, I have an NTSC tape for a movie (film). The tape is actually a PAL->NTSC transfer from 1990 or so, with no corrections for the PAL speed-up. I'm wondering if there's a way to slow the film back down to its original speed in a reasonable manner, presumably by adding a predicted frame every second. It doesn't have to be 100% perfect, just reasonably watchable.

To be clear, this is not a PAL source that I want to slow down. The speed-up is baked into the source. Short of finding a PAL copy of this film and running it through my PAL conversion scripts, this is my only option for watching the film in its correct speed.

Thanks.

[scharfis_brain]

You'll need to deinterlace and deblend (or in the rare case of pulldown: decimate) it from 59.94fps down to 25.00fps.
Afterwards you might do your desired slowdown from 25.00 fps to 24.00 or 23.976fps.

[jerrycan]

Good point. Thanks. I'll play around with my scripts and see what works best. Nothing's going to be 100% perfect but that's okay.

[pbristow]

I'm wondering if there's a way to slow the film back down to its original speed in a reasonable manner, presumably by adding a predicted frame every second. It doesn't have to be 100% perfect, just reasonably watchable.


It's very easy to overthink this task. The quick and dirty method (which usually works fine for me) is to simply slow it down by about 4%, and let my playback software take care of it. Assuming the current frame rate is 30 fps, you'll just want to drop it down to (24/25)*30 = 28.8fps.

You will likewise want to slow the audio down to stay in synch, i.e. from 48kHz to 48*(24/25) = 46.08kHz. Not many players will handle *that* weird sample rate without messing up the synch between sound and picture, though, so I would recommend then resampling the audio at 48kHz.

Stick your video and audio streams together in a suitable container format, and you're done! =:o}

The question now is whether your slowed down video will be acceptable to whatever you're using to play it back. I use PotPlayer, which copes well with anything I throw at it, but some players can be fussy about getting unexpected frame rates. And if you're planning to burn the results to a standard DVD, for example, then you will need to convert this "odd" frame rate to an acceptable standard one (25fps for PAL, 29.9-whatever-it-is fps for NTSC), either by duplication of existing frames (which is quick and easy, but causes rythmic motion-stutter) or some kind of interpolation. That's where things *can* start to get complicated, depending exactly on the characteristics of your source.

I do quick'n'dirty speed conversions quite often in good old VirtualDub, and watch the results in PotPlayer; I very rarely need to get Avisynth involved.

Of course, you may not need to do any conversion of your own at all: PotPlayer itself has built-in options for adjusting playback speed in in increments (I usually set it to 5% steps), with a choice of how to handle the audio speed/pitch issues according to whether the original speed-change was a pitch-preserving one or not, and whether you care... Or whether you'd rather put up with a few percent of pitch error than add an extra layer of destructive processing to the soundtrack that's already had quite enough damage done!

Using Potplayer's speed controls you probably won't manage an *exact* match to the original speed of the film, but a 5% slow-down (say) will get you a lot closer to the original speed than leaving it running 4% too fast.

Good luck! =:o}

[johnmeyer]

Why do you think you need to do anything? 24 fps film to PAL involves no "speed up" to the video itself. The PAL player just plays the 24 fps at 25 fps. There should have been no frames added, or deleted, or duplicated.

You need to post a clip so we can see what you are actually dealing with. If someone gave me a PAL movie, and if all the frames looked intact (i.e., no duplication or decimation), I'd then simply change the header in the video file to play at 23.976 or 24 fps.

[Emulgator]

jerrycan:
♩♪♫♬A sample, a sample, a kingdom for a samp...♩♪♫♬