Similar to 33fefdb4.
Fix trac ticket #4921.
Signed-off-by: Nicolas George <george@nsup.org>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 1acc90ea)

Conflicts:

	libavformat/tee.c
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>