"It's kind of like the big sites where you have to load the whole video before it'll start playing (no HTTP partials)."

It sounds like this is decribing the so-called "moov atom" begin placed at the end of the file.^1

1. https://www.adobe.com/devnet/video/articles/mp4_movie_atom.h...

If not, can anyone provide some examples of these "big sites". Would like to test.