Media Source Extensions

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Media Source Extensions (MSE) is a W3C specification that allows JavaScript to send byte streams to media codecs within web browsers that support HTML5 video.[1] Among other possible uses, this allows the implementation of client-side prefetching and buffering code for streaming media entirely in JavaScript. It is compatible with, but should not be confused with, the Encrypted Media Extensions specification, and neither requires the use of the other.

Netflix announced experimental support in June 2014 for the use of MSE playback on the Safari browser on the OS X Yosemite beta release.[2]

YouTube started using MSE with its HTML5 player in the September of 2013.

Browser support[edit]

  • Internet Explorer from version 11 on Windows 8.1. (2013 October) [3]
  • Google Chrome since early 2013, also on Android.[3]
  • Safari 8 on OS X/iOS 8.[3]
  • Opera since 9 June 2015.[4]

Firefox is the only major browser still without the full support for MSE, however a subset of the functionality is available for use with only YouTube in Firefox 37 on Windows Vista or later only.[5] Firefox added the same subset of MSE for YouTube playback support to Mac OS X starting in Firefox 38. [6]


  • bitmovin's bitdash MPEG-DASH player for HTML5 MSE and EME, with Flash fallback[7]
  • dash-js for HTML5 MSE [8]
  • dash.js for HTML5 MSE and EME [9]
  • rx-player for HTML5 MSE and EME (Live and On Demand) [10]


See also[edit]