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. 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.