Six months into the trial period for YouTube's subscription music service, the company is still working to create a service people will be willing to pay for. To that end, beta testers received an email today telling them their free subscriptions will be extended until September 15th. "As one of an exclusive group of Music Key beta users, your feedback has helped make it better each day," the email read. "And to thank you, we've got good news! Your free trial is being extended."

Music Key represents a major initiative from YouTube to build new kinds of products — and generate new revenues — around some of the massive buckets of content hosted on the site. It contains features for both free and paid users, starting with a top-level "Music" tab on YouTube for iOS, Android, and the web. Free users get access to ad-supported, Pandora-like "endless mixes" of songs. Members of the Music Key trial get ad-free songs and music videos, along with access to Google Play Music. The combined service will eventually cost $8 a month for the trial users.

Since launch, YouTube has been testing a variety of features for Music Key — some visible to users, and some behind-the-scenes changes to the infrastructure. The company's music catalog has expanded, and YouTube has improved battery drain and data usage. In an email, a YouTube spokesman said beta testers "have been a huge help in our goal of building the best subscription possible for both artists and fans. To thank them, we're extending their free trial, and we look forward to bringing this service to everyone." The company has previously said subscription service will be available to the public sometime this year.

Like YouTube, I also feel like Music Key isn't quite there. I'm a beta tester, and appreciate not having to watch pre-roll ads on Vevo clips any more. But I've had more fun using the complementary subscription to Google Play Music, which is faster and easier to use. (Being the world's biggest repository of videos of all kinds and a worthy competitor to Spotify simultaneously is a product challenge that I suspect would bring even the world's best software designers to tears.) On my phone, where I do much of my listening, clicking on YouTube's music tab shows me three endless-mix playlists and a single music video that my search history (correctly!) suggests I would enjoy. It's ... fine. But nothing I'd pay eight bucks a month for.

I suspect that YouTube is looking at the usage data for Music Key beta testers and drawing the same conclusion. (The company offered no comment on that front.) In any case, the company has just given itself another four months to figure it out.