HTML5 video
Support for HTML5 video has been steadily increasing. In June 2013, Netflix added support for HTML5 video. In January 2015, YouTube switched to using HTML5 video instead of Flash by default. In December 2015, Facebook switched from Flash to HTML5 for all video content.
Video email
Html4 markup language, in use since 2000, doesn't support multimedia elements natively. Html4 email systems typically simulate embedded video in email by having an embedded image (gif) which appears like a frame from a video. Clicking on the image causes a hyperlink to be launched in a browser window to display a video using the browser's video codec or a rich internet application like Adobe Flash. Many codecs and rich internet applications are not natively supported in browsers and require browser extensions to operate which can impede embedded video display.