Add 'mode' attribute to SourceBuffer, and support the ability to use and switch among 'sequence' and 'segments' appendMode. 'segments' is the default (and current) behavior. 'sequence' enables web developers to simplify some types of media streaming apps that use Media Source Extensions (MSE). 'sequence' appendMode allows more flexibility to maintain a gap-free buffered media timeline for web apps.
Docs: https://developers.google.com/web/updates/2016/03/mse-sourcebuffer https://developer.mozilla.org/en-US/docs/Web/API/SourceBuffer/mode https://msdn.microsoft.com/en-us/library/dn903679(v=vs.85).aspx