Spotify wants to be the world's music player. Its new streaming music widget, called the Play Button, is a step in that direction.

Unveiled Tuesday, the Play Button allows listeners to stream music on the Spotify desktop client via the widget placed on a web page. Play Button creators can choose any track, album or playlist to embed on web sites. Hopeful listeners who aren't yet Spotify users will be guided through the registration process.

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The Play Button debuts with some heavyweight partnerships. Some partners will make it easier for artists and consumers to post Play Buttons: Tumblr, FanBridge, FanRX and Most are editorial partners that will use the Play Button to increase visitor engagement. Their categories include music (Pitchfork, Rolling Stone, NME, Popdust, Spin, The Fader, Vice's, news (The Huffington Post, The Independent, the Guardian), entertainment (Time Out, Entertainment Weekly), pop culture (Elle, People) and technology (Mashable).

Spotify looked at the state of sharing music on the web and thought it could do better. "Streaming on the web was scattered, disparate and unreliable," Charlie Hellman, director of product development at Spotify, tells He singles out the annoyance of the embedded YouTube video that won't play because the content owner has demanded its removal. And he notes the frustration that can occur when a person isn't sure which of a web browser's many tabs is streaming music. "We actually do see a lot of utility in having a single music player to manage playback and keep things consistent and away from conflict," says Hellman.

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Streaming widgets are something of a throwback to an earlier era of digital music. In the middle part of the last decade, some people thought widgets would turn anybody with a web page into either a DJ (just put the widget at your MySpace page and you can potentially reach the entire world) or retailers (why go to stuffy iTunes when you can buy a track or album download from a BurnLounge widget placed on your favorite music blog?).

But the widget has taken two distinct paths since the MySpace days. Widgets continue to be valuable marketing tools. A variety of companies, from Topspin Media to ReverbNation, offer artists widgets that stream music, collect email addresses and drive traffic back to the artist or label website. The widget-as-storefront concept has evolved into Facebook apps and embeddable HTML that allows artists to place ecommerce modules at their websites.

Given the history of the widget, Spotify's decision to call its widget the Play Button was a good decision. The Play Button doesn't collect email addresses or sell digital or physical goods. It just streams music.

The Play Button partnership with Tumblr could pay dividends. A Tumblr user simply copies the URL or Spotify URI into a newly created Tumblr audio page, adds text and publishes the post. Each Play Button can be shared and re-blogged by other Tumblr users. "We anticipate there will be much more sharing of music across the network," says Danielle Strle, community team leader at Tumblr.

Streaming music isn't just promotional in nature, notes Gray Blue, Director, Music Industry Relations at FanBridge. "This is seriously an answer to the most continually asked question I've had for the last year and a half: How do I monetize Facebook streams?" FanBridge now allows its clients to easily add a Play Button module within the FanBridge Facebook application and, in effect, earn streaming royalties from their own Facebook pages.

Combined with its 10 million-plus active users around the world, these partners have the potential to help the Play Button become a familiar sight on the Internet. At least a minor level of ubiquity will be required for Spotify to enjoy the benefits of a network effect: the more Spotify's Play Button is seen online, the more new listeners will be attracted to the service, the more people and online properties will post Play Buttons, and so on. Competitive advantages are hard to come by in digital music, but a strong network effect is one of them.