I had problems with the adsense code not working in a drupal block.
Aparently you need to select as input format "php" instead of "full html" to make it work.
Good thing i trust google enough to try that.
Not sure why it's like this.

Usually people like and click more on the video ads. But Adsense decides what kind of ad will be on your site. So what can you do to increase your chances to get a video ad?
Well first you have to allow for image ads i think when you create the ad.
Second you have to have the correct ad size for video.
What are the adsense video format sizes?
 
Leaderboard (728x90)
Skyscraper (120x600)
Wide skyscraper (160x600)
Small Square (200x200)
Square (250x250)
Rectangle (300x250)