Rebuffering / rebuffer ratio
Rebuffering is a pause during playback when the video player runs out of downloaded video and must stop to load more. Rebuffer ratio is the share of total viewing time spent stalled in this way. For example, 3 seconds of stalling during 100 seconds of watching gives a rebuffer ratio of 3 percent. Lower is better.
Why it matters
Rebuffering is one of the most damaging playback problems, because it interrupts content the viewer already chose to watch. Stalls cut watch time, hurt ad completion and drive cancellations. Keeping rebuffer ratio low is often the biggest single quality lever for live sports and long-form services.
How it works
- The player keeps a buffer of downloaded video ahead of the current playback position.
- If the network slows and downloads fall behind, the buffer drains while playback continues.
- When the buffer is empty, playback stops and a loading icon appears until enough video arrives.
- Analytics tools add up stall time and divide it by total watch time to get the rebuffer ratio.
What is a good rebuffer ratio?
A good rebuffer ratio is well under 1 percent of viewing time, and strong services aim close to zero. Research found that stalling for just 1 percent of a video cut viewing time by about 5 percent. As an example, a ratio of 0.5 percent means about 3 seconds of stalling in a 10 minute view. Track how often stalls happen as well as their total length.
Why does my video keep buffering?
Video keeps buffering when it downloads more slowly than it plays. Common causes are a weak or congested connection, a player that picks a bitrate too high for the network, missing low-bitrate renditions, a slow CDN in the viewer's region and long segments that make quality switches slow. Adaptive bitrate streaming with a well-built encoding ladder fixes most cases.
Rebuffer ratio vs rebuffer frequency: what is the difference?
Rebuffer ratio measures how much of the viewing time was spent stalled, while rebuffer frequency measures how often stalls happened. For example, one 6 second stall in a 10 minute view gives a ratio of 1 percent and a frequency of 0.1 stalls per minute. Six 1 second stalls give the same ratio but six times the frequency, which usually feels worse.
Where it's used
Entertainment services, live sports streamers and video platforms treat rebuffer ratio as a core quality signal, because frequent mid-video stalls are one of the main reasons viewers stop watching.
Where it usually goes wrong, and how FastPix handles it
Teams often track only total stall time, which hides whether viewers had one long pause or many short ones. Stalls also cluster by network, region or device, which totals do not show.
For every view, FastPix Video Data reports buffer count, buffer fill (total stall time), buffer ratio and buffer frequency. These feed the stability score, the largest part of the QoE score, and can be broken down by ISP, CDN, device and country. That tells you whether a CDN, an ISP or a device is behind the stalls, so engineering time goes where watch time is being lost.
By the numbers
- In a study of 6.7 million unique viewers, a viewer whose video froze for 1 percent of its duration watched 5 percent fewer minutes than a similar viewer with smooth playback. (EurekAlert!: UMass Amherst and Akamai study of video quality and viewer behavior (2012))
