{"id":273,"date":"2020-11-29T15:39:33","date_gmt":"2020-11-29T20:39:33","guid":{"rendered":"https:\/\/www.alpharithms.com\/?post_type=term&p=273"},"modified":"2021-07-27T08:08:33","modified_gmt":"2021-07-27T12:08:33","slug":"dynamic-adaptive-streaming-over-http-dash","status":"publish","type":"post","link":"https:\/\/www.alpharithms.com\/dynamic-adaptive-streaming-over-http-dash-333915\/","title":{"rendered":"Dynamic Adaptive Streaming over HTTP (DASH)"},"content":{"rendered":"

Dynamic Adaptive Streaming over HTTP (DASH) provides access to multiple versions of files encoded in levels of quality. DASH allows clients to dynamically request different quality versions of parts of a file based on changes in network conditions.<\/p>\n

When connection bandwidth is high, a DASH client selects from higher-quality file versions. When the network is congested and speeds are slow, the client can request lower-quality versions of the file until network speeds improve.<\/p>\n

How DASH Works<\/h2>\n

DASH, sometimes referred to as MPEG-DASH, is an HTTP protocol and, as such, can be implemented on any webserver. There are three main components to a DASH-enabled service:<\/p>\n

    \n
  1. Different quality versions are stored for a file;<\/li>\n
  2. The server hosts a manifest file<\/strong> indicating URLs for different quality levels;<\/li>\n
  3. The Client uses a Rate Determination Algorithm<\/strong> to request the most appropriate quality level for a requested file.<\/li>\n<\/ol>\n

    Different Quality Versions<\/h3>\n

    The foundational concept of DASH is that a client can request a smaller version of a file when their network connection is slower than normal<\/a>. Or, in the case of many rural Internet customers\u2014they can request a lower quality version of a file\u00a0all<\/em>\u00a0the time<\/em>.<\/p>\n

    This enables clients to dynamically alter the quality of files being transmitted in response to changing network conditions without causing frozen frames or excessive loss of data. For example, a client could start streaming<\/a> a video in 4K resolution while the network is not congested, stream the next 5 minutes after a burst of network traffic at 720P, then return to the 4K stream after the network conditions settle. All this without the video pausing.<\/p>\n

    Manifest Files<\/h3>\n

    When a media server using DASH stores a file, it encodes multiple bit-rate versions and maintains a manifest file<\/strong> that can appropriately direct requests based on network speed. By using the Accept-Range<\/code> and Content-Length<\/code> HTTP headers, a client can request a URL for a specific quality encoding as well as a specific sequence of bytes from that file version.<\/p>\n

    When a client first connects to a DASH server, it requests the manifest file for whatever data it’s preparing to stream. Based on client-side bandwidth probing, the client then requests whichever version of the file is best suited for the available transfer speeds. Below is an illustration of what a manifest file might look like:<\/p>\n

    \"dash
    DASH manifest files map different segments of different file versions to URLs that can be requested via HTTP protocol<\/figcaption><\/figure>\n

    Rate Determination Algorithm<\/h3>\n

    A DASH client uses a rate-determination algorithm (a.k.a. adaptive bitrate selection) to determine the most appropriate file quality to stream. Different DASH applications rely on different RDAs to ensure optimal bit-rate version requesting.<\/p>\n

    For a detailed look at how these algorithms work, the variables they use, and their relative strengths, read the paper A Practical Evaluation of Rate Adaptation Algorithms in HTTP-based Adaptive Streaming<\/em><\/a>.<\/p>\n","protected":false},"excerpt":{"rendered":"

    Dynamic Adaptive Streaming over HTTP (DASH) provides access to multiple versions of files encoded in levels of quality. DASH allows clients to dynamically request different quality versions of parts of a file based on changes in network conditions. When connection bandwidth is high, a DASH client selects from higher-quality file versions. When the network is […]<\/p>\n","protected":false},"author":2,"featured_media":2472,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"inline_featured_image":false,"footnotes":""},"categories":[3,260],"tags":[461,78,131],"acf":[],"_links":{"self":[{"href":"https:\/\/www.alpharithms.com\/wp-json\/wp\/v2\/posts\/273"}],"collection":[{"href":"https:\/\/www.alpharithms.com\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.alpharithms.com\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.alpharithms.com\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.alpharithms.com\/wp-json\/wp\/v2\/comments?post=273"}],"version-history":[{"count":3,"href":"https:\/\/www.alpharithms.com\/wp-json\/wp\/v2\/posts\/273\/revisions"}],"predecessor-version":[{"id":279,"href":"https:\/\/www.alpharithms.com\/wp-json\/wp\/v2\/posts\/273\/revisions\/279"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.alpharithms.com\/wp-json\/wp\/v2\/media\/2472"}],"wp:attachment":[{"href":"https:\/\/www.alpharithms.com\/wp-json\/wp\/v2\/media?parent=273"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.alpharithms.com\/wp-json\/wp\/v2\/categories?post=273"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.alpharithms.com\/wp-json\/wp\/v2\/tags?post=273"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}