just to see if there any audio:
ffprobe -i in.mp4
find string as example here: Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 95 kb/s (default)
then exctract it
ffmpeg -i in.mp4 -vn -acodec copy out.aac
ffmpeg –help
-vn disable video
-acodec codec force audio codec (‘copy’ to copy stream)
https://www.linuxuprising.com/2019/11/ffmpeg-extract-audio-from-video-in.html