Alright, so I've been struggling with this issue for the past month, trying to read up on the technical details and figure out exactly what's happening, and why.
99% of my TV and movie library is in x264 MKV files running at 23.976p. This is just the default standard of such material. Even TV rips often appear to be reversed down to 23.976 even if they've been broadcast in NTSC. This is not a problem in itself, but in the two different players I primarily use, coupled with my TV, this presents an issue that is rather hard to properly circumvent.
Plex Media Player:
I've figured out that by syncing playback to display, meaning PMP speeds up video and audio to exactly 24p, and adjusting audio delay offset to about 200-250ms, I can get a smooth, judder-free output signal to my TV.
Apple TV 4 playback:
We all know ATV is 50/60p only, no proper 24p output signal. If my video content was running at exactly 24p, this likely would not be a major issue because my TV is capable of doing a reverse 3:2 pulldown from the 60p signal back down to 24p. The problem arises when combining the 3:2 pulldown scheme with a signal that isn't exactly 24p, leading to the TV first detecting a "hidden" 24p signal and then doing a reverse pulldown, but gradually falling out of sync so that about once every 15 minutes the image slowly gets very choppy, until it falls roughly into sync again.
Would it be possible, as in permitted by the ATV SDK and native services, to enable a toggle for display sync similar to how PMP does it? In other words, speed up video and audio to exactly 24p, and then letting ATV output it over the 60p signal as usual?
I'm not holding my breath for Apple to support 24p on ATV (even though I find it appalling that they don't when pretty much all video content they themselves sell or rent is 24/23.976p to begin with), but if a video player could perform some supporting "magic" to alleviate this problem, that would at least go a long way towards making the ATV 4 a proper, reliable Plex client platform.