An older Google Groups thread was just updated by Jeff Posnick the AdWords API Advisor, an official Google representative in charge of the AdWords API development and support. The Googler explains that the API Sandbox should now support the creation of video ads.

Now, simulating the addition of video ads may be supported in the AdWords Sandbox environment. Jeff Posnick explained:

So it should work, may not, but should. We know Google is at least working on making it work.

Also, Google released the NET Client Library 1.0.0 for the AdWords API v11 and v12.

Forum discussion at Google Groups.