Poor HAP performance in jit.movie~ and jit.movie

Hi. I'm trying to get better HAP performance in 8.1.11 in both jit.movie~ and jit.movie.

I'm getting delays/slowdown on loading of a movie, particularly when @loop 1 is used, as well as quite poor frame rates - as low as 13fps on a 25fps HAP movie. When I use the inspector, I notice that the engine selected for quicktime movies is either avf or vidll (this might be because hap is implemented inside vidll or avf, of course).

This is very noticeable when using @loop 1 - the start of each loop has a glitch. I'm playing back a very light file - 720p HAP normal, from an SSD. I've tried both GL2 and GL3, with no difference.

This is on macOS MBP 2015 15", both on the internal discrete Radeon M370X, and with a Vega64 egpu - both these should handle many layers of hap (and they have in the past - I've used HAP loads, just not since the start of the pandemic). I've checked the files are otherwise OK in other software.

Is there any advice about how to do this? I've had a look on the forum and there are a few grumbles about HAP playback, and general questions regarding looping... But nothing specifically about this, and I'm at a bit of a loss. Thanks!