YouTube is making its long expected foray into live streaming by launching an experimental trial with four new media partners. The new live streaming platform will be previewed in a two-day trial beginning Monday, but is expected to later grow considerably across the Google Inc.-owned website. Four YouTube partners will participate: the celebrity-focused Young Hollywood; the online television outlet Next New Networks; the how-to guide Howcast; and Rocketboom, the Internet culture vlog. For the last two years, YouTube has offered numerous events live, including a U2 concert, cricket matches in India and President Barack Obama’s first State of the Union address. But for all of those events, YouTube relied on third-party technology to enable the live webcasts. YouTube, though, is far from the first company to step into the streaming video space. Startups such as Ustream.tv, Justin.tv and Livestream have already established themselves. But YouTube remains the largest video platform on the Web and is expected to quickly become a considerable force in the rapidly growing live streaming video business. ComScore recently announced the amount of time American audiences spent watching the major live video publishers grew by 648 percent in the last year. The advertising possibilities are also good, since the average live streamed video view is 7 percent longer than the average online video view, according to ComScore.