I hope this question is appropriate here, sorry if not.

I'm currently seeing Star Trek (original series) for the first time after having watched The Wire and Dexter, and the contrast in acting techniques is extreme. Star Trek feels like watching a classic play, even ridiculously overacted at times, demonstrated by the episode "The Conscience of the King" where the cast is put next to a crew of Hamlet stage actors. (For the record, other series at the time are very much alike.) And while certainly not literally realistic, modern series have a much more life-like feel to them. Furthermore, there are some independent movies which experiment with actual realism today, something that would probably not have been thinkable in the earlier history of film.

Disregarding the advances in technology, what prompted this schism between stage and cinema / television acting? When and how did people first realize that cameras required a different style, and what were some milestone pieces I could watch to see that change?