Netflix has traditionally focussed on television screens, and for good reason. Around two thirds of all Netflix hours are viewed on traditional TV sets. But that is changing fast, and internally Netflix is increasing its efforts to give mobile viewers the highest quality video possible.
After enabling users to download content to their devices, and after "donating" servers full of content to ISPs globally to reduce the lag caused by it having to push data around the world by itself, Netflix appeared at Mobile World Congress in Barcelona this week to tell telcos and device-makers about its next step in embracing an increasingly mobile audience.
In two months, Netflix will switch to VP9, the open source video codec created by Google. The codec offers higher quality images than the current industry standard, h.264. Netflix took the switch in codecs as an opportunity to rethink the way it compresses video before it is streamed.
Ioannis Katsavounidis is a Senior Research Scientist at Netflix. Katsavounidis and his team have spent the last two years developing an aggressive new compression engine that goes shot by shot through content, rather than applying the same blanket compression to an entire file. Katsavounidis credits the new technique to two unlikely bedfellows: Bojack Horseman and Barbie.
When compressing Bojack Horseman, the brilliantly dark Netflix original series about a washed up former sitcom star, Katsavounidis noticed the company could achieve very high image quality with very little data. This is thanks to the simple colour palettes and large, low contrast images typical of a cartoon.
But another cartoon in the Netflix library, Barbie: Life in the Dreamhouse, was producing much larger files. Visually, an episode of Barbie was no more complex than Bojack save one recurring scene. Every episode of Barbie: Life in the Dreamhouse featured a scene with an explosion of glitter.
This one scene with a lot of colour and movement needed a high level of compression. In traditional video compression techniques, this meant the entire episode was compressed in high quality, just to accommodate that one shot.
Katsavounidis' team developed a way to break down the episode shot by shot, so every shot was evaluated and compressed separately, then reassembled into the final video file. Now, this one glitter explosion could spike the quality of that scene's compression, without spiking the entire file.
Next, hundreds of thousands of shots were shown to hundreds of viewers, who rated each shot on a variety of image qualities: colour, contrast, and sharp edges. This data was fed into a machine learning algorithm, which is now being used to recompress Netflix's entire catalogue.
Netflix demonstrated the new codec on a number of devices. Using the new codec and compression technique to show a video on a mobile screen, a 500 Kbps file was indistinguishable from a traditional high quality file, which used three times the data per second.
Even at 100 Kbps, the highest compression setting Netflix offers, video was sharp and detailed on a mobile screen. Normally video this compressed would look as blocky as Lego, but the video was entirely watchable, and in scenes from Stranger Things, you could still make out details like street signs clearly.
The author travelled to MWC in Barcelona as a guest of Huawei.
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