Revver are testing out a new CPM feature as another way for creators to earn from their videos, they play an ad pre-roll maybe post-roll as well, not sure, on videos 30 seconds or longer, it's still in testing.
With CPM you get payed for impressions, you don't have to rely on ad clicks, this is cool because if your able to just get lots of people to see your video and it has the CPM ad you make some cash. How much can you make from this new feature? I'm not sure, it all depends on how many people see your videos, I'd be happy with $2.00 per 1000 views, it certainly makes the whole video promotion a little more worth while, especially if you put all that work in only to have your videos "not take off", you'll get what you get from ad clicks plus impressions.
The only issue I have with it is that the pre-roll ads may be a little distracting, but I don't mind if I'm making a more cash from having them.
One last thing, if you don't want CPM ads in your videos you can opt out of having them, which is cool.