The following sequence is taken from the NTSC release of Lawrence of Arabia, Title 1, Chapter 15. It is the first 11 frames.

The first 5 frames are marked as interlaced (thanks!) and so the coded framerate is 29.97fps, but the material is clearly from 24fps source with 3:2 pulldown applied. The DVD then switches into progressive mode, and uses the repeat_first_field flag to offload the pulldown work onto the player. This switches the effective coded framerate down to 23.976fps.

In this DVD, small bits of scenes have been encoded at 29.97fps instead of always coding at 23.976fps. Why would they do this? One thought is that maybe certain scenes were touched up at video speed to remove objectionable artifacts in the pulldown conversion, but that doesn't seem to be the case here. I did notice that often we see some interlaced frames near the beginning of chapters. Maybe they fear some DVD players need time to switch into 24fps mode?

This came as a complete shocker to me. Here is some output of the first 150-or-so frames of The Good, The Bad, and the Ugly (1966). Take a careful look at all the non-repeat_first_field frames! They're interlaced! Not only that, but the progressive_frame flag is high the whole time!

The conclusion here is that a correct deinterlacer must look at _every_ non-repeat_first_field frame, even if we're clearly in a pulldown sequence! What a mess!

My biggest question here is why? Why would they ever do this? One observation we make is that every second frame is a blend of the two beside it. So, maybe the only print they found of the opening credits was at 12fps? Maybe it was originally recorded at 12fps and this is a conversion technique? Maybe the quality was so bad, they only decided to restore every second frame? If you have thoughts, please email them to me.