macos multichannel audio streaming (rtmp, ffmpeg)

alltogethernow.sh

## rtmp server
https://www.npmjs.com/package/node-media-server

### stream
# https://www.ffmpeg.org/ffmpeg-devices.html#avfoundation
# https://stackoverflow.com/questions/4716203/which-are-the-flv-supported-audio-types
# https://trac.ffmpeg.org/wiki/Encode/AAC
# https://trac.ffmpeg.org/wiki/SupportedMediaTypesInFormats
# https://trac.ffmpeg.org/wiki/AudioChannelManipulation
ffmpeg -f avfoundation -i "none:0" -f flv -c:a aac rtmp://localhost/live/test4ch

## record
ffmpeg rtmp:://localhost/live/test4ch