Netflix uses two different codecs to download its video content. Only Google currently supports the one that saves more space on the phone
This is one of the innovations introduced a few days ago along with the possibility of directly downloading video content on smartphones, and computers, to enjoy the shows not only more in streaming, but also to view them offline.
The possibility of being able to download individual episodes of its series to watch them more calmly at any time coincided with the launch of "Black Mirror". Netflix, therefore, tried to find the best method to avoid that the file of this, and other shows, "devoured" too much space on the phone. The main difference between watching a streaming video and downloading it offline is a matter of the codec used. If Netflix had only ever used H.264/AVC, it has now also introduced streaming and downloading in the VP9 format, an excellent open source video codec developed by Google. And so Android and Chrome users are at an advantage.
VP9 beats H.264/AVC
VP9, as mentioned, is an open source video codec developed by Google that uses a series of advanced technical devices for encoding with the aim of offering the same video quality but using a much smaller amount of data, or a much higher quality with the same amount of information required by H.264/AVC. The problem, as you can well guess, is that VP9 is not supported by everyone in the industry. It works, of course on Google products - so Android and the Chrome browser - as well as by a growing number of consumer electronics devices. iPhones, unfortunately, are cut off, and Apple hasn't yet spoken on a possible adoption of VP9 in the short term.
To each user his codec
Netflix, then, is obliged to provide streaming and downloads in different formats, even within H.264/AVC itself, depending on the user's profile, or rather, the device requesting the service. It uses, to get into slightly more technical details, streaming in H.264 AVC Main (AVCMain) for streaming from computers, and H.264/AVC High (AVCHi-Mobile) for mobile devices, which isn't as efficient as V9 (VP9-Mobile), but still saves a few bits.
The small-piece strategy
Netflix, codecs aside, is also coming up with tricks to encourage faster downloads, and thus also a smaller data footprint. The idea being adopted is to cut each video into chunks of three minutes each. The computer or device then analyzes the visual complexity of each clip and encodes them with the most appropriate settings. The bandwidth savings are significant: this method, compared to streaming - in combination with the new VP9 codec - saves about 36% of the data connection without the eye noticing. The savings with AVCHi-Mobile encoding, i.e. the one used by iPhones - is less: about 19%. An Apple user, in theory, could save five episodes of "Black Mirror", taking up the same amount of space, instead of four. Netflix is planning to adopt the same "block" technique for streaming viewing in the coming months.