Welcome to the forums.
While this is the forum for the WDTV Live (and you should be posting elsewhere) the question is general enough that you can get help here.
There are definitely switches that can do what you want, but my own advice would be to just buy a cheap AV receiver (Yamaha in particular makes some nice ones for less than $200) so that you can have superior sound as well as easy switching you can control with a remote (other manual switches, while far cheaper, are going to require you physically switch something each time). But that’s just me – sound is at least half the experience of a movie, and getting quality sound is at least as important as what you display it on (and no television has anything even slightly approaching quality sound).
Otherwise just google “AV switches” and you’ll find a ton of stuff.