As it works fine over http if mp4-files are done with mp4box -tight or similar way,
in most cases mp4-files aren't done like that and avformat works much better in those
cases (don't need to seek so much).
(cherry picked from commit 45f7ca3d6cff34b10f2cf314c15fca9066e8ccf8)
Signed-off-by: Pierre Ynard <linkfanel@yahoo.fr>