5 KPIs to Measure Video Quality of Experience & Why They Matter
Updated: Dec 2, 2019
Everyone has experienced poor quality video at one time or another. It’s painful to watch, and if you’re anything like me you’ll probably turn it off rather than suffer through it.
Slow load times, low resolutions, or even hearing the winning point on a sports event through your neighbors’ cheers instead of watching it happen in real time; these annoyances did not happen in the “olden days” of TV broadcast, but technology and habits have changed, and today most consumers will view at least one video each day through Over the Top (OTT) media services, aka streaming video. According to Nielsen seven out of 10 homes now have Streaming Video on Demand (SVOD) service and 72% use streaming-capable TV devices.
Besides annoying viewers, poor video Quality of Experience or QoE has a real effect on the bottom line for OTT and CDN providers that deliver the content. CDN company Akamai calculated that a single network-wide rebuffering event (think “loading loading loading”) of a certain video could lead to more than $80,000 in lost advertising revenue for the OTT provider. Of course, frustrated customers will eventually look to competing options, leading to customer churn and further revenue loss for both the OTT provider and the CDN.
One of the biggest challenges in improving QoE is how to measure it effectively, since, like anything, only if you measure do you have a chance of improving it. For consumers it’s relatively easy, “they know it when they see it” :). On a quest to put some quantitative values to this, some OTT providers have asked their customers to literally grade the quality of their video each day and submit it to them, on a scale of 1 to 5. But this is still qualitative and, incidentally, QoE can change in an instant due to network fluctuations, so should they report a 5 for when the video was streaming in HD or a 1 for when it got stuck, or a 3 to average out the day?
Measuring QoE is a challenge, but not impossible, and once one understands the key performance indicators of QoE and which are important to which types of video streams, the goal of achieving superior QoE grows that much more achievable.
Let’s look at the KPIs that matter for QoE:
Video startup time
This refers to how much time it takes for the video to start playing after the viewer has clicked on the selected content. This depends on many factors, from the bandwidth of the Internet connection, to how the video is encoded, to what else is happening on the local network at that time. If it takes more than a few seconds to start the video, viewers typically will abandon it. For better QoE, average video startup time needs to be as low as possible.
Streaming video is broken into small segments of a few seconds each. After the initial sections have downloaded and the video has started playing, the video player will continue to request new segments as the video progresses. However, if the network is congested, there is a chance that the video will display faster than the new segments can be downloaded. This leads to the dreaded rebuffering, or the video “getting stuck.” QoE aims for zero rebuffering, but is quantified by the rebuffering ratio, or percentage of time the video was rebuffering out of the total actual playing time.
Bitrate (kbps / mbps)
Most video is streamed using “adaptive bitrate” or ABR, which means that it can adapt itself to the changing congestion levels of the network. What enables this is that the video itself is encoded and made available in different bitrates. Bitrate should not be confused with the size of the Internet connection speed. While the size of the “pipe” connecting the device to the Internet does affect the bitrate that the video will play, and it represents a (highly!) theoretical maximum bandwidth, in reality the actual bitrate of the video stream will be affected by many more factors than the Internet connection. The higher the average bitrate per video, the better the QoE.
Higher resolution video appears smoother and brighter than lower resolution. A resolution of 1080 pixels is considered High Definition (HD), and there are even higher resolutions today for the larger viewing monitors. If your network conditions change in the middle of watching a video, your device may switch you from HD to a lower resolution and you will suddenly see poorer quality video. Bitrate and resolution are two sides of the same coin; usually in ABR implementations, a higher bitrate comes with higher resolution.
This is the bane of sports fans everywhere. Accustomed to truly live broadcasts on satellite or other traditional television media, people watching sports via live stream are out of sync with what is being reported on social media and with their neighbors who may be watching the same sporting event on a different medium. For close games, this can lead to major spoilers. One satellite TV provider capitalized on this to acquire new subscribers for the important World Cup games (aka Mon-di-al), capitalizing on the latency of their streaming competitors by naming it “Mon-delay.” The Reduction in time delay for live streams is an important part of QoE, but is much less crucial for other types, for example, Streaming Video on Demand.
The Streaming Video Alliance, an industry forum, has published definitions of the key network delivery metrics. Once you know the meaningful indicators for QoE, it’s time to start exploring how they can be improved, which we will do in future blog posts.