I'm like you on the tech stuff. Back when Tobe was working on the game, I had a problem where the game would crash almost every time an mp4 came up to the screen. He recommended I swap things out to webm to see if it helped. It worked exactly as he thought it would so I kept doing it. I was doing it manually by folder batch until that handy script was released.
There's a few things that were going on at the time.
1) Unity doesn't have a bespoke video player, it uses the video player of the OS itself. So, if the OS is a memoryleaky thing, you get Unity crashes trying to use it.
2) Unity 2019's had some sketchy releases where multiple games would be unstable.
3) No frame limiter was set in the code, which lead directly to CPUs going fully unthrottled like crazy leading to crashes as memory leaks cascaded faster than the garbage collector could collect.
Microsoft mostly solved the first (I never touched and cannot change the video player), Unity solved the second, and the third was an early hack before I started really making major changes.
" I don't understand all of the technical details, but with both my old and new laptops, I've had a hard time getting packs made from webm files to work properly. Sometimes they videos are "wavy-liquid" kind of blurry, sometimes they're just really low quality, and sometimes they're black and won't play at all. I'm MP4 all the way."
Windows has some issues with v8 because microsoft has investment in mp4, and windows doesn't have native support for v9 at all, which explains black window.
On the other hand, webm is a hard requirement on Linux, no other format besides webm, videocodec=v8, audiocodec=vorbis will work on that platform, and there's nothing I can do about that.