I'm pretty sure that it won't be legal in some or the work way. However, I want to clarify my doubt about legal issues again.
I read this article about it - is it legal to download youtube videos?
My plan is to create a software/app which has youtube-dl as a core piece to download videos from YouTube. It is open source and can be used commercially. Initially thought to have lot of features in the app for example playlists, but ultimately the app will download videos in user's desktop or mobile phones from YouTube via youtube-dl. Mostly it will be music download.
I'm thinking that the app creator will play a mediator role (between user and YouTube) when it comes to legal issues, as youtube-dl can be pointed in terms of backend legal issues and app users will be responsible to not share/distribute/reproduce the downloaded video, including other terms & conditions (if this statement is right).
Is it safe to assume that app creator will be a mediator and won't face any legal issues? This is my doubt.
In life this is not the case - As the mediator person who pick up drugs from one person and give to another person, is also considered as criminal.
On the contrary side - If a courier company (mediator) picks up drugs from one person and deliver it to another person (in a totally unidentifiable & protective wrapping which they cannot open legally), not sure they'll also be considered as criminals.
Not sure what to believe and should I go ahead to build such software & mobile app?