It will be useful in the upcoming transition to refcounted AVFrames.
Signed-off-by: Diego Biurrun <diego@biurrun.de>
This way we can directly remap channels from Opus' channel order to libav's internal channel order, instead of mapping channels from Opus' order to Vorbis' order then to libav's order. Signed-off-by: Diego Biurrun <diego@biurrun.de>