First of all how do you know it's true?

That being said, that makes zero sense. Just linking to a library, doesn't precluded using a protocol over a socket to talk to a graphic/audio server. Access control like remote code isolation (webAPIs), CORS and DRM also don't change anything about decoding and mixing video streams.

Well try and use yt-dlp to get an mp4 from YouTube that will open in quicktime. Can’t be done.

Haven't refuted that. I expect this to be due to an incompatible codec though, is it?

Update: https://news.ycombinator.com/item?id=44850435