CH_DIRECT_PAIR 929 libavfilter/avfiltergraph.c { CH_SIDE_PAIR, CH_DIRECT_PAIR }, CH_DIRECT_PAIR 932 libavfilter/avfiltergraph.c { CH_BACK_PAIR, CH_DIRECT_PAIR }, CH_DIRECT_PAIR 936 libavfilter/avfiltergraph.c { AV_CH_BACK_CENTER, CH_DIRECT_PAIR },