...user who wants to stay in their fedi app of choice (currently Moshidon) while enjoying multimedia content and not get booted out to a web browser every time I want to watch a video
It's for Lemmy rather than Mastodon, but that is basically why I put together Tesseract. It supports a lot of the "big" sources: Youtube (and both Piped and Invidious), Soundcloud, Bandcap, Spotify, Vimeo as well as Odysee, Peertube, and Songlink.
I think it's very important for fediverse mobile apps to support audio and video streaming to integrate with platforms like Peertube, Castopod, Bandwagon (once that gets going), etc.
I've already got Peertube supprt, but I'll definitely look into Castopod to see what, if any, embed API it supports and try to add that in. Same for Bandwagon, like you said, when it gets going. Thanks for that list.