Как комбинировать аудиолеги FFMPEG
ffmpeg -i shadowplay_file.mp4 -filter_complex "[0:a:0][0:a:1]amix=2:longest[aout]" -map 0:V:0 -map "[aout]" -c:v copy -c:a aac -ac 2 output.mp4
someone as lost as you