I looked into this yesterday and it appears to have been a change in how MPV is built when we upgraded it. Several things changed in MacOS rendering so I’m not totally surprised that something like this happened but we missed that it occurred because it was working (and seems we were testing on machines that were too performant to notice the change).
In short, if you use HTPC and look at the debug overlay, you’ll see videotoolbox-copy (the same occurs in Plex for Mac but you’d have to look at the logs to see this). That means it is using videotoolbox for hardware decoding (which is correct) but the -copy means the after the hardware has decoded the picture, the picture must be copied from the GPU to the CPU and then back to the GPU for display. This is why disabling hardware acceleration may help as it skips that first copy.
I’ve gotten the newer MPV to build locally enabling videotoolbox-gl which is MPV’s mechanism to display the decoded picture directly in OpenGL without the copy to CPU and back. This is what was used previously and got lost. It required some modifications to MPV as it seems that it was not intended to build with the option without building the standalone application whereas we just want the library.
