This isn't a bug report because technically it's working as intended, but I digress, I recently wrote a blog article about what video codecs work with VRChat. Trying to load anything but VP8 within the webm container gives the following errors when using the Unity Video Player:
Error: Unsupported video codec 'VP9' found <url>
Error: Unsupported video codec 'AV1' found in <url>
It's not that the system lacks the capability to play these, using AVPro or remuxing it into mp4 makes it play fine.
This is really annoying because it requires remuxing all open format content into mp4 for just compatibility with one of the two video players, it would be immensely helpful to be able to use webm files verbatim.