Just wanted to post an update.
About two hours ago, I finally figured something out, and I'm now on my way to porno bliss. I'm usually incredible with tech, but there's always something new to learn.
In my case, I had to learn that Apple devices (including the Vision Pro) can't handle HEVC MP4 files tagged as HEV1. The files need to be tagged "HVC1 to enable them to play nicely with quicktime" See my source on this.
All of the high resolution 7k and 8k VR porn movies I've downloaded are tagged HEV1. I guess there is technically some small differences between HEV1 and HVC1, but you can "remux" the files very fast (500x) to tag them HVC1. You need the ffmpeg command line tool (google it). Then, you can remux a file using a simple command like the following:
ffmpeg -i my_hev1_file.mp4 -c:v copy -tag:v hvc1 -c:a copy -c copy my_hvc1_file.mp4
Once I'd tweaked the mp4, I copied the file to the Vision Pro. If you need help with that, maybe just put the file into your iCloud drive because your Vision Pro should have easy access to your iCloud drive. I used a SAN server. Anyway, on the Vision Pro, you still need a video player that can play non-spatial VR files. Remuxing with the HVC1 tag isn't the same as re-encoding the file as an Apple spatial video---although that's possible, but a lot more time consuming. I'm using version 1.2 of that lame Reality Player, which cost like $9. I was going to ask for a refund, until I figured out the issue here was HEV1.
Good luck
