Because of political advertising relating to this year's elections, online video ad space is running out in multiple ZIP codes and content categories, according to Politico. Ad buyers in some locations are fretting because candidates have bought out much of the space available on sites such as YouTube, Yahoo and AOL.

"There has been incredibly strong demand for online video advertising inventory in targeted states, so there is virtually no 30-second inventory left for the fall," Rob Saliterman,an advertising industry professional, said to Politico. Campaigns are "buying it up for September and October and the first week of November."

It is not that all online video ad space is being taken up, just in key areas and for content categories like news and politics. As such, spots are being bought up months ahead of time, with late October internet video ad space estimated to cost three times the normal rate, according to Politico.

"[C]ampaigns and super PACs that are waiting on large-scale internet digital buys are really waiting at their own peril because they’re going to wake up in the middle of September and realize everything is already sold," Vincent Harris, a political consultant, said to Politico.

Already political ads are generating significant interest online. Six of the top 20 internet video ads from July were related to the upcoming presidential election, ReelSEO reported.