Say, I record a live mix I am doing at home for practice, using tracks which I have purchased. I would like to share this mix legally on the Internet. What are the copyright issues involved and how can I share the mix legally?
The first thing to say here is, I'm not a lawyer, nor do I play one on TV. Second thing to say... you should talk to a lawyer to answer questions about your particular situation definitively.
Having said that, I found a nice article about the various issues related to DJing, etc. I believe the bit below should be applicable to you, though I'd recommend reading the whole thing. Very interesting...
For each individual music piece you would have to determine what the license you obtained it from was, whether or not that license allows for derivative works from it and if not you need to get permission from the person or corporation that owns the rights to the work:
a) Is it licensed under Creative Commons? ( http://creativecommons.org/ ). If so does the chosen Creative Commons license allow adaptations? Or does it forbid it (Attribution-NoDerivs).
b) Is it in the public domain? Are you sure it is in the public domain? (Copyright laws changed recently, the musical piece might be public domain but the CD recording of a particular orchastra performing it might not be, etc.)
c) If it is not public domain or under Creative Commons who owns the publishing rights? Have you gotten their permission to use the material?
If you purchased all of the music then what I would do is contact the publisher of each piece of music for with a description of how you intend to use it and get written permission from them that it is alright to use it before posting it publicly online. If you are going to be making money off of selling the music or are going to be exposed to a large audience then you should probably consider getting a lawyer involved just to be safe.