Onimusha: Warlords doesn't even use H264 and has several other problems. None of these games need H264 to be explicitly exposed, they only need compressed output.
This merge request isn't about H.264; it's about compressed samples in general. 1/3 and 2/3 are here because H.264 needs slightly special treatment.
This is also only making my work on upstreaming Proton changes more difficult and I don't really understand what you are trying to achieve here.
The purpose of 3/3 is to fix bugs related to applications explicitly or implicitly assuming that the media source outputs compressed samples.
What changes does it make more difficult to upstream?