FRANKFURT/PARIS (Reuters) – Facebook (FB.O) is gaining ground on Google’s (GOOGL.O) YouTube as an outlet for big companies to market their products via online videos, the fastest growing category of Internet ads, a report published on Monday said. The competition for video viewers opens up a new front in the clash between the two web giants that already compete in other types of advertising given their appeal to young and international consumers, Ampere Analysis said in a study.