I haven't tested this, but YouTube appears to regularly use a parameter called "html5" in their URLs when you force a specific format. If your browser has Flash disabled, then whether you use "html5=0" or "html5=1" it plays in HTML5, but if you use a browser that defaults to Flash and add "?html5=1" to the end (if there are no parameters defined, that is, otherwise you put "&html5" on the end instead) then it does force the HTML5 format.
Try creating a rule that looks for the string "html5" in the URL parameters and redirects the user to the same URL but with that parameter added to the end if it isn't present. (Or perhaps you could simply add it to the URL of the same request, adjusting it at only the request layer before passing it through.)
Let me know how it works if you try it. I may end up experimenting with the same thing since it's not only safer and more supportable but lighter on bandwidth too.
Thank you for the hint.
I thought there is an easier way to make it work, but obviously I have to go deeper into the system than I have been so far.
The other thing is, I don't understand that the request from the client asking for flash, as YouTube for example offers HTML by default and otherwise if the client can't handle it offers to use flash instead.
Any idea why this happen? Basically if I can prevent this, most problems would be "solved" for me.
YouTube's default appears to be more complicated than that. As far as I can tell, it employes different defaults for different browsers. For example, on my PC, Firefox and Chrome both get HTML5 by default when I open videos, but IE gets Flash by default. All three browsers work just fine for both options on my system, so I suppose you'd have to ask Google for the real answer. lol
I did notice something interesting on my end when I tested further, however. In IE, when I force HTML5, videos play fine but I stop being able to load video ads. (That would be fine with me if it at least allowed me to skip them, but when I encounter a video ad I'm stuck permanently on that video.) I don't know if it's an issue with our MWG policy or if something else is in play, but in all of my testing I never was able to find the root cause. Perhaps this is why the default for IE is still Flash, eh?
I'm facing exactly the same behavior and was wondering why the HTML5 stream crashes after a while.
To be honest I wasn't thinking of the ads issue.
You are also right with the default player of ie11 which is flash. I will check to fix that via GPO settings, but anyway it will not solve the problem of the stopped HTML5 stream while playing.
I'm wondering what Microsoft say's about this behavior. Currently, for me it looks not that easy to ban flash out of ie11.