Ask HN: Issues with music and video related application

I have toying with an idea of building an application that is music and video related. This is first time iam venturing into building a product that is music and video focused. I was little worried about legal issues. So the question to HN is- •What are the issues one needs to be aware of before building product that is music or video related •Any open source web and mobile platform that I can use •Any general information that I need to be aware off.

Thanks