As Netflix at last gets around to offering downloads for offline viewing, the SVOD service is also rolling out some new video codecs to make the process more efficient for users.
In a recent blog post, Netflix detailed the advantages of AVCHi-Mobile and VP9-Mobile, two mobile codecs Netflix is using that it promises will provide new video compression formats, more optimal encoder settings and per-chunk bitrate optimization at about the same bitrate as its primary AVC-Main profile streaming.
H.264/AVC High profile and VP9 both offer bitrate improvements over AVC-Main, albeit with some tradeoffs. According to Netflix’s tests, High profile offers 19% bitrate savings as compared to the Main profile and AVC-High is supported by a whole lot of decoders across different devices. VP9, an open-source codec developed by Google, is mainly supported by Android devices and the Chrome browser. However, VP9 offers a higher 36% bitrate savings as compared with AVC-Main.
In addition to improved compression, the new codecs also help out with multiple enhancements to the encoding process. Perhaps more interesting though, is the per-chunk optimization technique Netflix is using for mobile encodes, which differs from the per-title optimization technique used for primary AVC-Main streams.
Netflix will essentially be breaking up titles into two to three minute pieces and individually analyzing each piece to assign the most appropriate encode setting. Combined with the new codecs, this technique is what allows Netflix to achieve such dramatic bitrate usage declines with VP9 while still maintaining high picture quality.
“Viewing it another way, members can now receive better quality streams for the same bitrate. This is especially relevant for members with slow or expensive internet connectivity,” wrote Netflix. “These gains represent noticeably better visual quality for the mobile streams.”
Netflix last month began re-encoding its catalog in order to achieve the new mobile bitstreams and for use in the new downloads feature. In addition to supporting the download feature, in the near future Netflix said the new bitstreams will be available for mobile streaming.