Adobe Flash Player
Steve Jobs also claimed that a large percentage of the video on the Internet is supported on iOS, since many popular video sharing websites such as YouTube have published video content in an HTML5 compatible format, enabling videos to playback in mobile web browsers even without Flash Player.
VP9
VP9 is implemented in these web browsers:
Internet Explorer and Apple Safari are missing VP9 support completely.
In March 2016 an estimated 65 to 75% of browsers in use on desktop and notebook systems were able to play VP9 videos in HTML5 webpages, based on data from StatCounter.