I have a machine with a media disk array that gets reads ~5.5GB/s. I also have a test file that is close to max bitrate(intense colour noise and a smoothness indicator) at 8192*2160@50 HAP. I can smoothly play 3 of these in TouchDesigner, 4 occasionally chokes as it's pushing the disk limit. In MM I can only play one, a second copy playing in tandom gets seriously choppy with stalls of .5s etc, unplayable. This is both with and without the hardware decode box checked, with nothing else going on(just two standard quads).
My question is why such a drastic difference in playback performance?
As you can imagine the test file is enormous and not practical to send through, if you have a commercial TD license I can give you the project to render it out on your end.