Starting with 2:2:2:4 cadence and ending with 24fps?

[Asterra]

Got my hands on a low-effort pressing of an old serial on bluray. Quality of the individual frames is actually not bad. I can tell it probably really is something above NTSC. Unfortunately, everything about the actual bluray mastering is borked. For one thing, they stuffed 4 hours onto a single 25GB layer, and gave the entire video 10Mbps to work with, at a constant bitrate.

But the main problem is that they mastered it at 29.97fps which of course means 1080i with a temporal resolution of 59.94fps. (Actual scan type listed as MBAFF.) The final cadence is 2:2:2:4, or 1:1:1:2 depending on how you want to look at it.

I've tried tinkering with ffmpeg's mpdecimate function, and while I can get a result that does whittle it down to 24fps, it also discards every sequence of frames that are duplicate, even when they are things like static digital title cards, and I can't seem to pin down thresholds that sidestep this result. Though it would be better if there were a function that was designed to assume a steady cadence for the entire video rather than proactively hunting for that cadence every frame.

Suggestions?

[jagabo]

The regular decimate filter should work for that.
https://ffmpeg.org/ffmpeg-filters.html#decimate-1

[Asterra]

The regular decimate filter should work for that.

Does seem to work, at least for a test snippet. Knock on wood.

Since I'm having to re-compress the video anyway, I want to get the best quality out of the result that I can. In your opinion, what would be the best codec/preset/whatever to go with? It's fairly grainy black and white film.