I definitely see how youtube-mp3 would be infringement since they are the ones actually sending you the bits over a wire. I have a hard time seeing how youtube

I definitely see how youtube-mp3 would be infringement since they are the ones actually sending you the bits over a wire. I have a hard time seeing how youtube-dl would even count as unauthorized copying. Not just in an "it's virtually unenforceable" sort of way, either. If it's unauthorized copying to use software on my computer to download and store copyrighted bits that I obtained directly from the authorized source (in this case YouTube), then Google would need to help go after themselves, since Chrome is doing the same thing (as youtube-dl). If I can create/use a CLI tool that (presumably) acts like a browser (youtube-dl) and you can't implement a way to prevent that, then that's your issue -- not mine. Legally, I'm probably wrong, though, since intent is usually way more important than what you actually do (e.g. porn vs nude art). EDIT: looks like others pretty much confirmed this thought process in the time it took me to write it.