(defun my-browse-url-mpv (url &rest args)
  (message "Opening URL in MPV...")
  (start-process "mpv" "*mpv*" "mpv" url))

(defun my-browse-url-mpv-looping (url &rest args)
  (message "Opening URL in MPV [looping]..." url)
  (start-process "mpv" "*mpv" "mpv" "--loop" url))

(with-eval-after-load 'browse-url
  (add-to-list 'browse-url-handlers
               '("youtu\\.be" . my-browse-url-mpv))
  (add-to-list 'browse-url-handlers
               '("youtube\\.com" . my-browse-url-mpv))
  (add-to-list 'browse-url-handlers
               '("youtube\\.com/shorts" . my-browse-url-mpv-looping)))