It should be noted that it is not Netflix's intention to save space on mobile devices with these new compression formats. So, if you were previously downloading 1 episode of a visually heavy TV series in a given amount of space on your mobile device, you could now download 2 episodes in the same space, without compromising on the quality of the video. Hence pre-chunk encoding results in optimised encoding for every 1 minute to 3 minute long chunk of content, resulting in lighter downloads for some of Netflix's content. So if there’s a graphically heavy action sequence in a movie, it will contain more information that a scene with shots of an ocean or a forest. Sequences and scenes in a movie usually store varying amounts of information. What this essentially does is that it breaks up a movie into different parts for encoding. The company does so by using a method called pre-chunk encoding. This format dramatically reduces amount of data used (15% to 19% in bitrate savings). On the other hand the VP9 compression format is not supported by iOS devices or the Safari browser.įor iOS devices, Netflix used another compression format called H.264/AVC High profile.
VP9 results in an average of 36% bitrate savings as per tests conducted by Netflix. The same is also supported by the Chrome browser, Firefox, Opera and Microsoft Edge (but not internet explorer).
As VP9 is a royalty-free lossless compression format which was developed by Google, it is supported by all Android KitKat 4.4 and above mobile devices. So how has Netflix optimised downloads? The company says that they have adopted two new compression formats for their media library H.264/AVC High profile and VP9 (profile 0). Bitrates can be increased to subsequently get excellent video quality, but that will result in large files and would require sufficiently more storage space. Usually, higher bitrates correspond to better video quality and common practice is to encode at lower bitrates progressively, until a noticeable quality loss in the video occurs. Here, bitrates refer to the amount of data that is stored for every second of media that is played. H.264/AVC Main Profile was created to provide good video quality at lower bitrates. Traditionally, Netflix video streams are compressed using the H.264/AVC Main profile, a very popular video compression format which is commonly supported by various web browsers, mobile devices and televisions.
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