This is a temporary workaround until someone add support for f4v.

Work-around #4915
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>
(cherry picked from commit f47133cbac88a1ef04e526df27eaa4e86a6f2d5a)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>