Honestly, while that is definitely an issue, even greater is the danger of feeding realistic fake videos via social media. People will believe whatever they want to believe, but now they have a video proving that Bush orchestrated the 2001 attacks on the WTC / Moon landing was filmed in a studio / Obama is secretly gay / insert your de-stabilizing video here.

There are already products to detect fake videos / images but:

a) there's no money in it (or at least, a LOT less than making fake videos)

b) it will always be in catchup mode with the latest and greatest fake techniques