This field is a uint16_t, see docs:
http://opus-codec.org/docs/opus_in_isobmff.html#4.3.2Signed-off-by: Dale Curtis <dalecurtis@chromium.org>
Reviewed-by: James Almer <jamrial@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>