ffmpeg: map 4 stereo pairs into 7.1 audio in FLV/RTMP
The inputs option in ffmpeg filters refers to number of streams, not channels.

ffmpeg -protocol_whitelist file,udp,rtp -threads 4 -loglevel info -i /tmp/sdp -filter_complex '[0:1][0:2][0:3][0:4]join=inputs=4:channel_layout=7.1[a]' -map 0:0 -map '[a]' -c:v copy  -c:a aac -b:a 384k -ac 8 -ar 44100 -f flv URL