Encrypted Media Extensions
Netflix supports HTML5 video using EME with a supported web browser: Chrome, Firefox, Microsoft Edge, Internet Explorer (on Windows 8.1 or newer), or Safari (on OS X Yosemite or newer). YouTube supports the HTML5 MSE. Available players supporting MPEG-DASH using the HTML5 MSE and EME are NexPlayer, THEOplayer by OpenTelly, the bitdash MPEG-DASH player, dash.js by DASH-IF or rx-player.
Adobe Flash
Representing open standards, inventor of CSS and co-author of HTML5, Håkon Wium Lie explained in a Google tech talk of 2007, entitled "the  element", the proposal of Theora as the format for HTML5 video:
I believe very strongly, that we need to agree on some kind of baseline video format if [the video element] is going to succeed. Flash is today the baseline format on the web. The problem with Flash is that it's not an open standard.