From the AMA:

    As far as I understand, basically the same way YouTube and
    Vimeo are: DMCA safe harbor laws, plus paying streaming
    royalty boards etc. We're also trying to get direct deals
    with all the majors too, but those negotiations take a looong
    time. It was a couple years just to get EMI signed.

So it looks like they only have an EMI deal right now but other labels are in progress.