Depends on site, niche, quality of traffic (i.e. people actually buying from the advertiser from your site), etc. You might want to appeal to the networks with your statistics similar to Machinima. If you are the top dog in your niche and I mean top site on Alexa and top searched popular site for your main keyword set then you can charge what you want. If you are going through a cpm video ad network to earn then forget it. You won't make 10% of what you would make reaching out to advertisers yourself.