Emacs Lisp: Extract all the audio from a file or directory of files

audio.el

(defun extract-audio (choice)
  "Extract the audio from a chosen file or directory of files."
  (interactive "fVideo File or Directory: ")
  (cond ((file-directory-p choice)
         (thread-last (directory-files choice 'full)
                      (seq-filter (lambda (file) (not (file-directory-p file))))
                      (mapc #'extract-audio-from-file))
         (message "Done converting: %s" choice))
        (t (extract-audio-from-file choice))))

(defun extract-audio-from-file (file)
  "Extract the audio from a given video FILE."
  (let* ((file   (expand-file-name file))
         (audio  (audio-format file))
         (target (file-name-with-extension file audio))
         (result (doom-call-process "ffmpeg" "-i" file "-vn" "-acodec" "copy" target)))
    (pcase result
      (`(1 . ,_) (error "Failed to convert: %s" file))
      (`(0 . ,_) (message "Converted: %s" target)))))

(defun audio-format (file)
  "What is the audio format of the given video FILE?"
  (let ((result (doom-call-process "ffprobe" file)))
     (pcase result
       (`(1 . ,_) (error "%s is not a video file." file))
       (`(0 . ,out)
         (string-match "Audio: \\([a-z]+\\)," out)
         (match-string 1 out)))))

Note: this requires at least Emacs 28.1 to use file-name-with-extension. Usage of Doom Emacs is also necessary if you want to use doom-call-process, which is a very convenient wrapper around calling shell processes.