Smule has invested heavily in its social network for music lovers, and now it is making one of its biggest investments yet by adding video song-sharing to its Sing! Karaoke app.

Now fans can sing video duets together, even if they are not singing at the same time. Smule lets fans do an open call, where someone sings their version of a song. Then someone else who answers the open call can sing their version of the song. Then Smule uses its technology to merge the separate videos into a single duet video. The players can then share the duet, and the community can upvote it if it’s a good performance.

This kind of innovation in digital music is one reason why the Smule Nation social network has more than 40 million people who have created songs together. Each day, people sing or play more than 4 million songs using a variety of Smule’s apps. Every other day, they upload a terabyte of their songs to Smule’s network. If I were to do this, it would be “over sharing.” But you’d be surprised at how talented some of the best-rated singers are, said Jeannie Yang, chief product officer at Smule, in an interview with VentureBeat.

“We think the video duets will make the network much more social,” Yang said.

Smule’s network is a participatory one. You can create and join songs. You can tap on your iPhone and begin a session that captures a video of your performance. You can invite others to join and thereby produce a whole series of duets with just one of your own performances. Smule automatically mixes and renders the duets with transitions.

The tech pushes your iPhone to the edge, as Smule streams video and audio down from the cloud. In parallel, it captures video and audio on the device and synchronizes the two streams in real-time. Smule also uses its expertise in audio processing to create the duets so that you don’t have to spend a lot of time editing videos yourself. Smule pushes new devices such as the iPhone 6 to the limit of what they can do, in terms of processing power.

Jeannie Yang of  Smule

Above: Jeannie Yang of Smule

Image Credit: Dean Takahashi

The Smule Nation social network includes music created by fans of Smule’s apps, including MagicPiano, Ocarina, I Am T-Pain, Guitar!, and Sing! Karaoke. More than 125 million listeners have created more than 1 billion songs using Smule’s apps. In some of those apps, users are singing or playing tens of thousands of songs every hour. That is happening even though maybe 10 or 15 percent of the people who use an app will ever upload something.

Jeffrey Smith, chief executive of Smule, said in an interview that the company has ramped up its cloud infrastructure to handle the load of activity. The company has more than 200 servers in Mountain View, Calif., and in San Francisco.

“We’ve been figuring out how to handle this surge that we’ll get from the video duets,” Smith said. “We think this is going to deliver better experiences with video for people.”

Smith said the company expects to double sales from $21 million to $40 million this year, with revenue from 250,000-plus paying subscribers and advertising too.

Smule was founded in 2008 by Smith, a Stanford University doctoral student, and Stanford assistant professor Ge Wang. The company’s investors include Bessemer Venture Partners, Granite Ventures, Shasta Ventures, and Floodgate. Smule has more than 100 employees in San Francisco.

“Things are working, as we have a lot of people pushing content up into the cloud,” Smith said. “People are losing their inhibitions around music, and that’s why we founded the company. It’s an exciting time for us.”

Weekly subscriptions for access to video and platform features of the social network cost $2.99 a week. You can join a video duet for free, but to start one, you have to be a paying subscriber. Roughly 2 percent of those users are signing up for subscriptions, Smith said.

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