The first set iterates through all standard FFmpeg layouts and checks that those which fit MP_NUM_CHANNELS succeed. The second set iterates through built-in named channel layouts, and attempts to convert them to AVChannelLayouts.
The first set iterates through all standard FFmpeg layouts and checks that those which fit MP_NUM_CHANNELS succeed. The second set iterates through built-in named channel layouts, and attempts to convert them to AVChannelLayouts.