>>310283225
I made this ffmpeg-python script to stitch together all the video and concatenate the audio tracks in mono:
https://pastebin.com/EbdBj3q5
ffmpeg-python is great, it's a million times better than squinting at the -filter_complex language and escaping filenames to get the subtitles burned in. The screens are split with this uv offset shader https://pastebin.com/ewdX9wCJ , then you just wire in all the audio sources to the unity video player component. Unfortunately, the new udon video player doesn't properly assign separate audiosources, so I fell back to sdk2.

For streams, the same trick should work in the stream player or the AVPro udon player, but you'd be limited to only two separate audio tracks (left and right channels) unfortunately. And you'd have to mux together the video streams as well. Combined with the 10 to 30-sec delay on HLS-based streams, it's not going to be a great experience. 

The new vrchat update ostensibly supported RTSP streams (1 sec delay), but it's broken right now for dumb reasons. I'm waiting for another update to test the feasibility of low-latency streams, which will make things like jackbox games a lot more feasible.