There's no such thing as free streaming music, but Rdio might have gotten one step closer with the release of its freemium service Thursday morning. Hoping to compete with music platforms Spotify, which has free-ish option, Rdio one-upped the competition offering an even freer option. "No registration. No credit cards. No downloads. And best of all, no ads," Fast Company's Austin Carr explains. "The San Francisco-based startup is providing instant access to its catalog of more than 12 million songs. For no cost." This "no cost" business sounds like hype to us. And it turns out it is. Rdio will fulfill your free streaming music fantasies, but only for a limited time.

How it's free: No ads, no credit card requirements, unlimited streaming. The only thing required to sign up is an e-mail address or Facebook account, as Venture Beat's Devindra Hardawar points out. "The free service requires just an e-mail address or Facebook account to sign up--there’s no credit card required. That’s a wise decision, since it completely removes the barriers users previously had to check out the service." Then you can listen to the entire Rdio service sans naggy ads or music caps. Bomb. 

How it's freer than Spotify: Spotify too has a "free" option, which offers unlimited streaming of its 15 million songs, compared to Rdio's 12 million, with ads. That lasts for six months. After that it caps the music at 10 hours per month, which is teeny tiny--barely more than a work day. Rdio, on the other hand, doesn't cap hours of music and doesn't have ads. But beyond these music caps, it provides freedom from Facebook's shackles. Spotify requires a Facebook account, Rdio presents it as an option. 

How it's not free at all: And here come the limits. While there are no hour caps, Rdio has a mysterious music cap, explains Lifhacker's Jason Chen. "The limitation comes with the amount of music you can listen to, and you'll be able to see how much free music is left in your month by a meter at the top of your profile page." It gets even worse: Rdio will not disclose if that limit will look like the entire Abba collection, or just Abba Gold. But Chen says it will work something like this:

The company will track how much usage it takes to convert a free user to a paying customer. That means if a freemium user barely takes advantage of the offer from month to month, Rdio is less likely to limit usage--there's still the opportunity for he or she to get addicted to the service. But if a user continues to max out usage each and every month, it's clear that user is not so likely to become a paying customer. 

Once users hit the mystery cap, Rdio has no problem kicking them off. "After a certain amount of time, if someone is not willing to pay, we're going to be faced with having to tell them that their free use is up--if they want to keep going, they'll need to pay," CEO Drew Larner told Carr. 

And, like Spotify, the free service is only available with Rdio's desktop versions. Regular rates apply for the tablet and mobile apps. For some unknown yet restricted time, Rdio's service is indeed freer than Spotify. After that: Freeloaders will want to reconsider the options.