In sample [muxing.c](http://ffmpeg.org/doxygen/5.1/muxing_8c-example.html), [AV_CHANNEL_LAYOUT_STEREO](http://ffmpeg.org/doxygen/5.1/group__lavu__audio.html#ga59db80472380a3c66c52f2296232244d) is used. But I cannot find the definition in java lib.