YouTube's subscription music streaming service, Music Key, won't be released to the general public until at least September, Google has revealed.

The company sent a letter to Music Key's beta testers notifying them of the revised release date. The company now says Music Key will be released on Sept. 15.

"We’ve got good news!" Google wrote to the testing group. "Your free trial is being extended." Music Key is expected to feature both free and paid tiers -- with the paid tier offering users commercial-free streaming of music videos. The service also allows users to play streaming music from YouTube in the background on a mobile device, and to download music videos to play offline.

Music Key subscribers also become subscribers of Google Play, as Lifehacker pointed out last year. Like Spotify, Google Play combines access to a vast library of songs with discovery-oriented playlist features.

It's clear from Spotify's move into video last week that YouTube already has serious competition in the music + video streaming space. Luckily for them, YouTube is already far and away the biggest music streaming service in the U.S.

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