CH_DIRECT_PAIR 863 libavfilter/avfiltergraph.c { CH_SIDE_PAIR, CH_DIRECT_PAIR }, CH_DIRECT_PAIR 866 libavfilter/avfiltergraph.c { CH_BACK_PAIR, CH_DIRECT_PAIR }, CH_DIRECT_PAIR 870 libavfilter/avfiltergraph.c { AV_CH_BACK_CENTER, CH_DIRECT_PAIR },