FFMPEG
Install package
# apt install ffmpeg
emerge -av ffmpeg
- Convert any to any
ffmpeg -i file.mp4 file.mp3
- Record monitor 2 desktop
ffmpeg -y -video_size 1920x1080 -framerate 30 -f x11grab -i :0.0 -vsync 0 -c:v prores -f alsa -ac 2 -i default result.mkv
A player is recommended
Try MPlayer or MPV to play video files and listen to online radios
MPV can be used to listen youtube video-audios.