Reject streaming .mp4 files over http that are not muxed reasonably.

Audio and video samples must be reasonably close by at any given timestamp,
for now we define "reasonably" as "their offsets must not be more than 1MB apart".

related-to-bug: 3509977
Change-Id: I4c3a2a239bf911306833f3b17b73c9e2f76ab901