The youtube vid seems to act the same for mobile mobile safari and pwa–you can’t play it in the background or on lock screen. That could be bc youtube is unique (they block background playing unless you subscribe to youtube premium, for example, and that could have impact here).
Here’s some other examples:
Vimeo embed:
And audio embed:
I find that both work as I have described on iphone:
–on mobile safari access, you can play both in the background and on lock screen (only difference is that the video stops playing when the phone changes state to lock/background, and you have to hit play again)
–on pwa access, neither play in background or lock screen (there is no further play option in either case once app goes to background or phone goes to lock screen)