Interpolate duplicates in hybrid video?

[embis2003]

I have a few VOBs ripped from a DVD that are hybrid; 23.976 with duplicates for film sections and 29.97 for video sections. As I know there are 3 ways to deal with this. Convert to 29.97 for smooth video but jerky film, convert to 23.976 for smooth film but jerky video, or vrf in mkv with timecodes. But I was thinking of a fourth option. Perhaps someone could write a script that could simply replace the duplicates in the film sections with interpolated frames for a constant 29.97 all throughout without having to get into nasty VFR. Maybe this already exists and I don't know it but if not, I wouldn't know where to begin to make a script that could function that way. Of course, I suppose you could do it manually with SVPFlow...

[johnmeyer]

First of all, there should be no duplicates in the film sections unless the film was something other than 24 fps. If it is silent amateur film than it might have started out at 15, 16, or 18 fps (common silent amateur film speeds). If it is sound film, then it should be 24 fps, and should have no duplicates.

So, what is the source of this film, and what sort of duplicates are you seeing? Can you post a sample that is cut, but not re-encoded? 5-10 seconds is adequate, as long as it contains a reasonable amount of motion (no talking heads, please).

You can certainly synthesize intermediate frames to go from 23.976 up to 29.97. There are dozens of scripts based on AVISynth's MVTools2, and also on SVP and Interframe, both of which are derivatives of MVTools2. For some types of motion this interpolation can be near-perfect. For other types of motion, it can create artifacts.

Here is an early 1940s parade, taken at 16 fps, which I interpolated up to 30 fps in order to reduce judder. It will probably look wonderful when you first view it, but if you look long enough, you will begin to see the artifacts. For this clip, I decided it was a reasonable tradeoff because the judder was pretty pad as the camera panned to follow the parade participants.

https://www.youtube.com/watch?v=t8HjRN0rw5M

[jagabo]

Perhaps someone could write a script that could simply replace the duplicates in the film sections with interpolated frames

That produces 29.97 fps overall but the frames aren't evenly spaced in time. The first 4 frames of a 5 frame group represent 1/23.976 second intervals but interpolated frame will represent a 1/47.95 second interval. Playing all 5 frames at 1/29.97s intervals will still result in jerky motion. What needs to be done is to interpolate motion over all 4 frames into motion over 5 frames. You can easily do that with a number of motion interpolation filters (svpflow, mvtools, etc.). But the motion interpolation often doesn't work well, producing gross distortions and/or blending.

Here's an example where you can see gross distortions from doubling the frame rate with motion interpolation:

https://forum.videohelp.com/threads/352741-Frame-interpolation?highlight=tron#post2215502

23.976 to 29.97 will suffer similar defects, though a little less so.

[manono]

The whole DVD is progressive? Progressive 23.976fps with dupes to bring it up to progressive 29.97fps? And then the 29.97fps sections are also progressive? If so, that's unheard of in my experience.

Or when you say, "29.97 for video sections", does that mean it's interlaced?

Anyway, do you have a short sample showing both kinds? I agree with jagabo that interpolating the dupe frames will still leave it jerky, if somewhat less jerky.

[jagabo]

I assume he's talking about the same videos in his other posts. And some of the shots in those videos are telecined film overlaid with 30p titles. If you make them 24p the titles will be jerky. If you make them 30p the underlying video will be jerky.

[embis2003]

Perhaps someone could write a script that could simply replace the duplicates in the film sections with interpolated frames

That produces 29.97 fps overall but the frames aren't evenly spaced in time. The first 4 frames of a 5 frame group represent 1/23.976 second intervals but interpolated frame will represent a 1/47.95 second interval. Playing all 5 frames at 1/29.97s intervals will still result in jerky motion. What needs to be done is to interpolate motion over all 4 frames into motion over 5 frames. You can easily do that with a number of motion interpolation filters (svpflow, mvtools, etc.). But the motion interpolation often doesn't work well, producing gross distortions and/or blending.

Here's an example where you can see gross distortions from doubling the frame rate with motion interpolation:

https://forum.videohelp.com/threads/352741-Frame-interpolation?highlight=tron#post2215502

23.976 to 29.97 will suffer similar defects, though a little less so.

If that's the case, than never mind. If motion will still be jerky the whole concept is worthless. I decided to just go with 23.976 and the jerkiness wasn't that bad with video sections.