Does the PPP mechanism support offline music? If PPP only supports online music, I think its experience is very bad and will be unpopular. Because that could mean loading slow (or even interrupted), high traffic (in our country, high traffic means high prices), low music quality. Or should I ask, does The Musicoin have other music payment mechanisms? Look forward to your answer.

This is a great question, thanks.
PPP is a base contract to regulate playback ,actually it doesn't need to be online to be executed as Musicoin blockchain supports offline or pay-later transactions. For an offline scenario, the only thing needs to do for the apps(e.g. mobile app, or desktop app) is to prepay a special PPP license(for offline playback) and cache the content accordingly. The app should be able to gauge the consumption and eventually report back to blockchain once it gets back online to fulfill the transaction.
So far, Musicoin system didn't have this special contract yet, but it's definitely possible in theory and will be there. We are very happy to hear some coiners here ask this type of question. We really welcome you to the slack.musicoin.org have further discussions.