Company says counting error had no impact on other video metrics or billings

Facebook miscalculated the average time viewers spent watching videos on its site, drawing fire from big ad buyers and marketers.

Facebook Inc. on Friday apologized for overestimating a key video metric for two years, a miscalculation that irked advertisers and media companies that have poured resources into video efforts on the social network.

Facebook likely overstated the metric by between 60% and 80%. That discrepancy means that marketers could have misconstrued the performance of video ads, affecting their decision making when it comes to spending money on Facebook versus competitors like YouTube, Twitter or even television.