Preview at WWDC likely in June, followed by September launch.
Apple Posts WWDC 2012 Session Videos for Developers
With over 100 sessions available, the videos are a significant resource for those looking to learn more about developing for OS X and iOS. The quick turnaround on posting the videos is helpful for developers who were unable to attend WWDC, especially given that the conference sold out in less than two hours this year.
Apple used to charge several hundred dollars for the videos, but ended that practice in 2010 as the company restructured its developer programs to lower the cost of entry and its increasing popularity led to conference sell-outs that prevented some willing developers from attending in person.