In an experiment with the Media Capabilities API, YouTube saw a 7.1% increase in MTBR with only a 0.4% decrease in average resolution of videos served.
The Problem #
Typically, media sites have several variants of each video that they can present to users, encoded in different frame rates, resolutions, and codecs. Until recently, web developers had to rely solely on isTypeSupported() or canPlayType() to determine whether each variant could be played in an individual user’s browser. While this told the developer whether media could be played at all, it didn’t provide an indication of playback quality, such as whether there would be frame drops or device battery drain. Without this information, developers either had to create their own heuristics or just assume that if a device could play a codec/resolution combination, it could do so smoothly and with power efficiency. For users with less capable devices, this often led to a poor experience.
The Solution #
The Media Capabilities API allows websites to get more information about the client’s video decode performance and make an informed decision about which codec and resolution to deliver to the user. Specifically, the API provides the developer with an estimate of the smoothness and power efficiency of a particular codec and resolution combination. This allows the developer to avoid scenarios where the client is likely to have a poor playback experience.
In Chrome, the Media Capabilities API uses metrics from previous playbacks to predict whether future playbacks in the same codec and at the same resolution will be smoothly decoded.
YouTube Case Study #
YouTube used the Media Capabilities API to prevent their adaptive bitrate algorithm from automatically selecting resolutions that a device could not play smoothly.
Users who were part of the experimental group collectively saw less frequent rebuffers (the mean time between rebuffers, or MTBR, increased by 7.1%) while the average resolution, measured by video height, served to the aggregate group only declined by 0.4%. The substantial increase in the MTBR with the small corresponding reduction in average resolution indicates that this change significantly improved quality for a small subset of users who previously had a poor experience.
Check out the official sample to see how the Decoding Info API works.