With European online video ad spending set to more than quadruple in the next five years — nearing €1 billion in 2013 — the majority of publishers have now set their sights on the in-stream video ad opportunity. Advertisers prefer pre-roll ads to other in-video ad formats, and users are actually as likely to accept pre-roll ads as any other format publishers can use to monetize video content. Sites can balance the needs of advertisers and users by limiting both in-stream ad frequency and length and by rotating through a variety of in-video ad formats.