Youtube is used horribly by advertisers. Don't make a video ad that plays before the content that people can't wait to click Skip. Just make a video that's entertaining/informative and post it to youtube. People will share it for free and watch it willingly.
I work at an advertiser. Most so called "viral" ads we've researched involve significant levels of paid impressions before they got to a "viralable" level. There ain't no such thing as a free lunch. Also it's significantly difficult to make a highly entertaining ad as well as convey your product benefits/superiority at the same time - strains creativity of the ad agencies though some are adapting faster to the online…
You can't even pay to have people watch your ads anymore. Isn't this the death of the industry as we know it?