Make/keep playback window smaller

When you play a new video through itunes, it always makes the size the same (more than half the screen). You can shrink the size, but if you are playing a series, then when it auto-plays into a new video, it resizes it back to the original size.

Is there a way to either make the default play size smaller or at least make it so in a playlist, the window stays the same size throughout?