@Anthony Monda @Erik Krane Langhaug - I checked in with the folks on our team who are the experts in this area (@Amit Rajput and @Saili Raje).
In Stream when you play a video we always do adaptive bitrate streaming so the user doesn't have to download the entire video (only the parts they play) and so we can adjust the quality/size of the video depending on the user's available bandwidth. In addition our videos in Stream are always secured with AES-128 bit encryption. We use encryptiong to ensure that as we deliver videos over the internet, caching devices, and CDNs, only users who are authorized in Stream for a specific video will be able to get the key to decrypt it. As such to do the above in HTML browsers without Flash/Silverlight we rely on a feature of browsers called MSE. MSE was never back ported to Windows 7 + IE 11, it was only pushed back to Win 8.1+. Thus the only way we can accomplish both adaptive bit rate streaming and our encryption on IE11 + Win 7 is with the use of Flash.
We are guessing that YouTube is able to play back VOD in this environment because they maybe don't encrypt their streams? It's our understanding that for VOD in order to feed in the video tag to do pure HTML playback without MSE, (since you have no control of it) you can only pass in unencrypted chunks.
