Faculty Recruiting Support CICS

Ramesh Sitaraman's research shows how poor online video quality impacts viewers

Associate Professor Ramesh Sitaraman and collaborators at Akamai conducted the first large-scale study of its kind to quantitatively demonstrate how video stream quality causes changes in viewer behavior. "Anyone who provides online video content, from the major news channels to sports and movie outlets, is worried about such things as a video failing, how fast a video starts up, whether it freezes, and how such loss of quality affects viewers," says Sitaraman.

"Content providers want viewers to not abandon their videos, want viewers to watch longer, and return often to watch more videos, resulting in more opportunities to show ads and to increase their subscriber base. The link between video streaming quality and viewer behavior has long been recognized as hugely important, but we couldn't study it with any scientific precision until now."

"The ability to collect lots of relevant data, and new methods we developed for their analysis were the game changers," says Sitaraman, who is an Akamai Fellow recognized for his past role in helping to create the Akamai network that now serves 15-30% of the global web traffic and helping pioneer content delivery networks now used to stream a large fraction of Internet videos.

In a recent paper presented at the ACM Internet Measurement Conference, Sitaraman and his co-author S.S. Krishnan report that viewers begin to abandon a site if the video does not start up within two seconds. Beyond two seconds, every additional one-second delay resulted in roughly a 5.8% increase in the abandonment rate. They also found that viewers are less tolerant of startup delay for short videos such as news clips compared to longer ones such as movies. And viewers with better connectivity abandoned a slow-starting video sooner. Further, a typical viewer whose video froze for 1% of its duration watched for 5% fewer minutes, and a viewer who left the site after failing to play a video was 2.3% less likely to return to the same site within a week.

This study analyzes an unprecedented 6.7 million unique viewers from around the world who in aggregate watched 23 million videos for 216 million minutes. To conduct this research, Sitaraman and colleagues devised a novel technique based on Quasi-Experimental Designs (QEDs), an approach more familiar to medical and social science research than to computer systems research. They assigned viewers to one of two "treatment" groups. One had a good quality video viewing experience while the other group experienced poor quality such as video failure to launch, delayed start, or repeated freezing.

A viewer in a good quality group was then randomly matched with a viewer in the poor quality group so that the paired viewers had the same geography, connection type, content and other characteristics of interest. "By comparing the difference in behavior of the paired viewers for hundreds of thousands of pairs, we are able to better isolate the impact of quality alone and exclude other confounding factors," says Sitaraman.

He adds, "A scientific understanding of the causal impact of streaming quality on viewers is a key piece of the puzzle for the success of online media. It helps computer scientists build better-distributed networks that deliver videos with higher user-perceived quality. Research in this area is particularly important now as even traditional media like television are migrating quickly to the Internet and more than 85% of consumer traffic on the Internet is predicted to be video-related by 2016."


Ramesh Sitaraman was interviewed about his study examining tens of millions of online video streams to determine how video stream quality impacts viewers. His work is the first large-scale study to quantitatively demonstrate that viewers abandon videos that do not startup quickly, that they watch for fewer minutes if videos freeze, and that they return less often to watch more videos at a web site if they encounter failures.

In 2013, this research was the focus of a front page Boston Globe article and was also featured on NPR's Morning edition:

Boston Globe Front Page:http://www.bostonglobe.com/lifestyle/style/2013/02/01/the-growing-culture-impatience-where-instant-gratification-makes-crave-more-instant-gratification/q8tWDNGeJB2mm45fQxtTQP/story.html?s_campaign=8315

NPR Morning Edition:http://www.npr.org/2013/01/10/168974423/in-video-streaming-rat-race-fast-is-never-fast-enough

Prof. Sitaraman presented his online video quality research at the ACM Internet Measurement Conference in November.

More details in the UMass Amherst press release: UMass Amherst Computer Science Research Quantifies How Online Video Stream Quality Affects Viewer Behavior. You can also read the video streaming publication.

A number of media outlets have posted this latest news:

Boston Globe: Fall 2012 article

CNN: Online viewers ditch slow-loading video after 2 seconds

Gigaom.com: Online viewers start leaving if video doesn't plan in 2 seconds, says study

PC Magazine: Study: Online Video Viewers Start Leaving After Waiting Two Seconds 

CNET Australia & Yahoo!: Viewers give up on online video after two seconds of loading 

The Droid Guy: Study shows streamers abandon videos after 2 seconds of buffer

Hindustan Times: Internet video viewers have a two-second attention span

The Verge: Study: viewers have no patience for buffering, abandon videos after two seconds of waiting