December 6, 2016
Last week, Netflix opened the doors to downloaded content for offline viewing on mobile devices. Now, the company is describing some judicious technology adjustments it made to ensure viewers enjoy an improved video image, and that the resulting content doesn’t eat up the mobile device’s storage. The company did that by switching video codecs, although the result favors Android users, as well as improving its already-established method of varying data rates based on the needs of each scene in a movie or TV show.
According to Variety, Netflix has been using the H.264/AVC codec almost exclusively for streaming video. Now, most Android users who download video content will see the results of VP9, an open source video codec developed by Google. VP9’s specialty is to use “advanced encoding tricks to deliver the same video quality with significantly less data,” or improved video quality “with the same amount of data.”
Apple, however, doesn’t support VP9 on iPhones and “has given no indication that it plans to support VP9 any time soon.” For Apple mobile devices, Netflix will encode downloadable programs with another version of H.264/AVC (“High” rather than “Main”), which “isn’t quite as effective as using VP9, but still allows Netflix to shave off some bits.”
The company also amped up a technique it developed for video encoding that varies the number of bits used vis-à-vis specific scene demands. An action scene, for example, requires more bits to encode all the visual information than a static shot or an animated movie. Netflix began doing this last year, enabling delivery of “better-looking streams to users with slower Internet connections while saving up to 20 percent of data.”
For downloadable video, Netflix is now dividing videos into one-to-three-minute chunks, so the program can be optimized for visual complexity on a more granular level. Using this method with the new VP9 codec saves 36 percent of bandwidth on average, without negatively impacting the video quality.
Videos encoded to Apple mobile devices via H.264/AVC High, can save “up to 19 percent less bandwidth on average,” not as good as VP9 but still better. In any case, both methods also help consumers stay below their monthly data cap. Variety states that, “Netflix plans to bring both chunk-based encoding as well as new encoders to mobile streaming in the coming months as well.”