Nielsen to Begin Tracking Viewership of Videos
Marketers like Nielsen's service because it gives them a metric that is comparable to audience ratings in television which Nielsen has long supplied. Advertisers can make a similar comparison using comScore's metric, which is known as Validated Campaign Essentials, but some advertisers already have a relationship with Nielsen for other services and don't want to use two measurement firms.
Google's refusal to accept Nielsen's tags upset those advertisers, media buyers say, particularly as some marketers don't want to accept Google's own measurement of ads running on YouTube.
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