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HTTP Live Streaming (also known as HLS) is an HTTP-based media streaming communications protocol implemented by Apple Inc. as part of its QuickTime, Safari, OS X, and iOS software. It is similar to MPEG-DASH in that it works by breaking the overall stream into a sequence of small HTTP-based file downloads, each download loading one short chunk of an overall potentially unbounded transport stream. As the stream is played, the client may select from a number of different alternate streams containing the same material encoded at a variety of data rates, allowing the streaming session to adapt to the available data rate. At the start of the streaming session, it downloads an extended M3U playlist containing the metadata for the various sub-streams which are available. Since its requests use only standard HTTP transactions, HTTP Live Streaming is capable of traversing any firewall or proxy server that lets through standard HTTP traffic, unlike UDP-based protocols such as RTP. This also allows content to be offered from conventional HTTP servers as origin and delivered over widely available HTTP-based content delivery networks.〔(MPEG-DASH vs. Apple HLS vs. Smooth Streaming vs. Adobe HDS )〕 HLS also specifies a standard encryption mechanism using AES and a method of secure key distribution using HTTPS with either a device specific realm login or HTTP cookie which together provide a simple DRM system. Later versions of the protocol also provide for trick mode fast-forward and rewind and integration of subtitles. upLynk has also added the AES scrambling and base-64 encoding of the DRM content key with a 128-bit device specific key for registered commercial SWF applications together with a sequential initialization Vector for each chunk to its implementation of the standard. Apple has documented HTTP Live Streaming as an Internet Draft (Individual Submission), the first stage in the process of submitting it to the IETF as an Informational Request for Comments. However, while Apple has submitted occasional minor updates to the draft, no additional steps appear to have been taken towards IETF standardization. ==Architecture== HTTP Live Streaming uses a conventional web server to distribute audiovisual content and requires specific software to fit into the proper format transmission in real time. The service architecture comprises: ;Server :Codify and encapsulate the input video flow in a proper format for the delivery. Then, it is prepared for distribution by segmenting it into different files. In the process of intake, the video is coded and segmented to generate video fragments and index file. : * Encoder: codify video files in H.264 format and audio in MP3, HE-AAC or AC-3. This is encapsulated by MPEG-2 Transport Stream to carry it : * Segmenter: divides the MPEG-2 TS file into fragments of equal length, kept as .ts files. It also creates an index file that contains references of the fragmented files, saved as .m3u8 ;Distributor :Formed by standard web Server, accepts requests from clients and delivery all the resources needed for streaming. ;Client :Request and download all the files and resources, assembling them so that they can be presented to the user as a continuous flow video. The client software downloads first the index file through a URL and then the several media files available. The playback software assembles the sequence to allow continued display to the user. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「HTTP Live Streaming」の詳細全文を読む スポンサード リンク
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