Are you talking about youtube-dl? They find a way to fuck it up every 3-4 weeks or so, so the maintainers find a way around the block, then you have to use "youtube-dl -U" to upgrade to something that works to download videos. If it's a music video and you just want the audio, "ffmpeg -i greatmusic.mp4 greatmusic.mp3" although it's not always as good as no compression.