This is mostly useful if the hw accelerator cannot handle the stream.
The software decoder fallback will then use frame multithreading if it
supports it.
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>
(cherry picked from commit b72986e83bad854b2db4a0e7e1d4e54be5140179)
Signed-off-by: Jean-Paul Saman <jpsaman@videolan.org>