How can I use a single ffmpeg or ffplay command to play two audio files at the same time, but through different output devices?
As is documented, this command plays a single audio through the output device with index 1:
ffmpeg -i audio.mp3 -f audiotoolbox -audio_device_index 1 -
But how can I play two at the same time? Without using two commands (because eventually I want to arrive at a filter suitable for mpv synchronous playback https://superuser.com/a/1325668/325613)