This is required when encoding audio in libav 0.8, otherwise
it will crash due to a division by zero.
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>
(cherry picked from commit 25fc1243b81a46a100e37db5ec477bd5096b979a)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>