[FFmpeg-user] How to extract audio from video without re-encoding?

[inhahe]

I want to extract audio from any arbitrary video file and have it save to
an audio file without re-encoding and without me knowing ahead of time
which audio file format to use.

I don't know how to do it because ffmpeg requires an output filename with
an extension, which means I have to specify the audio file format within
the command. I want ffmpeg to choose the audio file format for me based on
the type of audio embedded in the video, much like the -x parameter does in
youtube-dl.

How can I do this? Thanks.