The IAB is tightening up standards for web video ads:
Now, Web publishers that have received official video measurement certification from The Interactive Advertising Bureau (IAB) must disclose that they employ auto-start video, and just how they use it. But the IAB is not trying to eliminate auto-play video altogether.
However, per the IAB’s new guidelines, “Web sites [are not required] to disclose the presence of auto-play if users have a reasonable expectation that they are entering a video environment.”

