[vim_wannabe]

Adaptive streaming sure, but can you not handle the different audio combinations using source-tags? And HEVC/VP9 with h264 fallback I would imagine is the primary use case they (WHATWG?) were thinking of supporting when creating the source tag.

[prebrov]

Technically you could have a single URL that returns any manifest based on user-agent or whatever player info is available in the GET request.

But yeah, JS players make life a whole lot easier by providing a single API for customisation, handling media source extensions and a bunch of other stuff.