Debateable: the play button does press in when playing ... I'm not sure which is better.

I meant that button has name "play" by default. If I want to play content I press this button. Button name should change from "play" to "pause" or "stop" while playing content. Press "pause" (stop) button stops playing content and should return name to "play"

I think "pause" should be better, because preview is not rewinding to beginning. Preview freezes at place where you pressed button

I thinkt this would be good for the player as well. Either have it constantly as "Play/Pause" or change it to "Pause" while content is playing.