Is your feature request related to a problem? Please describe.
When using Hubs for a presentation or watch party, the current Focus mode is

1. not immersive, as you don't see the virtual world nor other avatars
2. not as usable as a standard videophone app: the video by default is smaller than the window and text chat can't be seen

Describe the solution you'd like
Focus mode for videos should (on personal computers and mobile) overlay the video over the virtual world, at the video's natural resolution, and be located in one corner of the window (probably the upper left). This would allow as clear as possible view of the video, without fiddling with the zoom, not break immersion, and allow text chat to be usable (unless the user's window is very narrow).

Separately, when a video starts to play, users should receive a tip that they can type "F" to focus it (unless that tip has been presented to them recently).

Describe alternatives you've considered
A stopgap measure might be, in Focus mode, displaying the video so it fills the height or width of the window.
Currently, worlds should probably place 2-D Media Frames above eye level, like a movie theater, so users can readily see it past other users.

Additional context
This UI might be better for Focus mode for all 2-D media.