Bookmarklet

Drag this button onto your Bookmarks toolbar: Converto.io DL

Click Converto.io DL while watching a video on YouTube to download it as MP3 or MP4

Alternative way to download from YouTube

While watching a video on YouTube:

Add "conv" (without quotes) before "youtube.com" or "youtu.be" in the URL

Press Enter

Choose conversion format to convert YouTube video to MP3, MP4 or GIF