AAC_CHANNEL_BACK  258 libavcodec/aac.c     decode_channel_map(new_che_pos[TYPE_CPE], new_che_pos[TYPE_SCE], AAC_CHANNEL_BACK,  gb, num_back );
AAC_CHANNEL_BACK  305 libavcodec/aac.c         new_che_pos[TYPE_SCE][1] = AAC_CHANNEL_BACK;  // back center
AAC_CHANNEL_BACK  308 libavcodec/aac.c                                  = AAC_CHANNEL_BACK;  // back stereo