By expand feature, do you mean "Fullscreen" mode??
That options comes along with the other controls by the browser itself, so we can't remove it.
But the video should have been centered in full screen mode.
Can you share the video so that we can test it out?
Its just a normal mp4. Tested it with a bunch with the same result.
Please upload it to dropbox or anyother online storage service, and send us the link so that we can test it out.
Are you saying for every video, you are having the same result?
In that case, can you tell us which browser and its version are you testing it on??