The copyright laws are somewhat confusing but here is my take
on it.  You can record any music being played in a public venue
such as a public park, public street, band organ rallies, etc.
You can post the video on the Internet but you cannot profit
financially in any way.  Credit should be given to the performers
or group.

If you want to polish your videos with music before posting to
the web you might consider purchasing a license.  I have used
http://www.naxoslicensing.com/  NAXOS maintains a vast store of
music, from rock to classical, for example:
http://www.youtube.com/watch?v=PzFh2ngxp58
 

Peter Vander Veld