The source of where this video was recorded is unknown at this point, but it looks completely legitimate. You may need to turn your volume all the way up to get a good listen at the voice cast but you can easily spot how good the animation looks on here.
The Dark Knight Returns stars Peter Weller (Robocop) as Batman.
Batman: The Dark Knight Returns is a four-issue comic book limited series comprising The Dark Knight Returns, The Dark Knight Triumphant, Hunt The Dark Knight and The Dark Knight Falls, written and drawn by Frank Miller, originally published by DC Comics under the title Batman: The Dark Knight in 1986