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.
MuseScore
MuseScore.com allows playback of a score in any browser supporting the HTML5 audio tag. A score can also be linked to an online video, so that one may follow the sheet music while watching a video featuring that score.