Zencoder
Zencoder is the creator of an open-source HTML5 video player, Video.js, built with Javascript, HTML, and CSS. Video.js plays video via native playback in all HTML5 browsers and devices, or through Adobe Flash when HTML5 playback is not available.
HTML5 video
Apple still only supports H.264, but Microsoft now supports VP9 and WebM, and has pledged support for AV1.