Index: src/wp-includes/js/mediaelement/wp-mediaelement.js
===================================================================
--- src/wp-includes/js/mediaelement/wp-mediaelement.js	(revision 29991)
+++ src/wp-includes/js/mediaelement/wp-mediaelement.js	(working copy)
@@ -28,6 +28,10 @@
 			}
 		};
 
+		// mediaelement needs the height that wp sets on .wp-video to correctly size the player
+		// but the container height should be set to auto for responsive video embeds
+		$('.wp-video').css('height', 'auto'); 
+
 		$('.wp-audio-shortcode, .wp-video-shortcode').mediaelementplayer( settings );
 	});