So called “engagement advertising” or “transactional advertising” encourages users to participate voluntarily in advertising by watching a sponsored video (a.k.a. commercial), or alternatively downloading an app, taking a poll, or interacting with a site. In exchange, users get access to things they would usually have to pay for.

Many Facebook apps, including those from top developers like Zynga and Causes, already work with companies like SocialVibe and TrialPay directly. They pay users in their app-specific virtual currency or in real dollars donated to charity.

Now, users will be able to watch video ads in order to earn Facebook’s platform-wide virtual currency, which they can then presumably spend across other Facebook apps.

Facebook said its goal with the program was to get more people to start using Facebook Credits and carry a Credits balance.

Facebook Credits are mostly spent on social games but they are increasingly accepted for other types of transactions, like videos and deals. One Facebook Credit is worth $0.10.

Please see the disclosure about Facebook in my ethics statement.

Image via Inside Facebook.

The company now occupies a top-floor office–complete with wraparound views and a deck–that was, in fact, recently left unoccupied by the departure of a Japanese hedge fund, said Causes co-founder and Joe Green when NetworkEffect visited him there this week.

It’s a bit incongruous, but Green says the rent is cheaper than a crappy office near Twitter’s in San Francisco’s SOMA neighborhood, the far hipper place to house a start-up these days.

Causes has, since 2007, been trying to facilitate activism and philanthropy by connecting users to non-profits and one another. Backed with some $16 million in funding from venture capitalists like NEA and Founders Fund, Green wants to make the non-profit world more of a marketplace, where organizations compete for givers’ participation and dollars.

Charity–worth $300 billion annually in the U.S., compared to $12 billion for the music industry–is the “last industry not revolutionized by the Internet,” Green said.

Causes has always been tightly linked to Facebook (Green shared a dorm room with the founders at Harvard), and is “in many ways one of the great survivors of the Facebook platform,” said Green, having grown to 150 million users originally as a Facebook app and now as a Web site powered by Facebook Connect.

Of those 150 million users, about 1 million have ever made a donation on Causes, and 12 million have signed a petition. Causes would obviously like to figure out ways to get more people to participate meaningfully.

In many ways, the trajectory of Causes mirrors that of social games, the most successful category built on top of Facebook to date. They are both inherently viral, built around users inviting their friends.

But in some ways games are actually beating Causes at its own game. Zynga on Monday announced it had raised $3 million for recovery efforts for the recent Japanese earthquake and tsunami, from a combination of virtual goods bought by its players and a physical bracelet bought by fans of Lady Gaga. Zynga has raised more than $10 million for charitable causes since 2009.

Causes, meanwhile, has raised some $30 million since 2007, and $800,000 this month for tsunami relief efforts in Japan.

But it’s a bit unfair to just compare dollars to dollars. Causes enables users to connect to more than 25,000 different non-profits and participate by doing things like signing petitions rather than just donating money. It’s a richer experience than buying a virtual doodad.

Even so, it’s obvious that games have figured something out. So Causes recently enlisted three social game monetization partners: TrialPay, SocialVibe and SupersonicAds. The companies offer Causes users video ads that pay out $0.10 to a chosen cause every time a user watches.

So instead of giving money, users can “give a minute” to charity. In early tests, Causes users have exhausted the company’s video ad inventory on a daily basis.

Enlisting simple online actions that trigger a charitable donation isn’t a new concept–see, for instance, Freerice.com–but it’s interesting that Causes is going directly to social games’ transactional advertising providers.

“We’re not trying to become a gaming company, but there’s some interesting similarities there,” said Green.