Slightly modified the original script to use Streamlink and lower quality to 240p for bandwith and resource purposes.
(require 'elfeed)
(defun elfeed-v-mpv (url)
"Watch a video from URL in MPV"
(async-shell-command (format "streamlink -p mpv %s 240p" url)))
(defun elfeed-view-mpv (&optional use-generic-p)
"Youtube-feed link"
(interactive "P")
(let ((entries (elfeed-search-selected)))
(cl-loop for entry in entries
do (elfeed-untag entry 'unread)
when (elfeed-entry-link entry)
do (elfeed-v-mpv it))
(mapc #'elfeed-search-update-entry entries)
(unless (use-region-p) (forward-line))))
(define-key elfeed-search-mode-map (kbd "v") 'elfeed-view-mpv)