What's more, the average online video lasted about five minutes, and those who watched ad-supported content sat through an average of 24 seconds worth of commercials. With a little help from YouTube, Google led the way in total viewership last month, serving video to over 144 million unique viewers. Those consumers watched over 1.9 billion videos out of the nearly 4.9 billion watched in the U.S. across all video services last month, according to comScore.