[Bug 20336] Revert addition of keySystem attribute to HTMLSourceElement

https://www.w3.org/Bugs/Public/show_bug.cgi?id=20336

--- Comment #5 from Aaron Colwell <acolwell@google.com> ---
(In reply to comment #4)
> It doesn't matter too much to me - the primary downside is the extra work
> for implementors. How important is the declarative case given that many
> (most?) EME apps will use MSE as well? 

I think you need to be careful about assuming that MSE & EME will always be
used together. I can easily see web applications wanting to protect their
content without going down the adaptive streaming path.

> 
> I'm a bit concerned that the same logic (type + key system) needs to be
> spread across objects to support both <source> and
> MediaKeys::isTypeSupported(). I don't have experience to say how big of an
> issue that is, though.
> 
> If this makes sense for EME, does it make sense for MSE as well? I guess the
> assumption there is that you either support MSE for ISO/WebM or you wouldn't
> support any such extensions to HTMLSourceElement. Browsers that don't
> support MSE might get an automatic fallback without needing to make any
> changes, though. (If there is interest in this idea, we should file a
> separate bug for MSE. I'm just bringing it up here for context.)

You can't use HTMLSourceElement with MSE because you have no way to determine
what the URL would be at page generation time. Even if we used URLs w/ a
special scheme to signal MSE usage, most existing browsers would fail on those
URLs because they don't understand what the URL is trying to convey. I tried
going down this path early in MSE's life. I gave up on it because the fallback
behavior for browsers that didn't support MSE wouldn't actually work. :/

In the case of EME though it is possible to have valid URLs that the browser
understands, can try, and are available at page generation time. I'm pretty
sure existing browsers would ignore the keySystem attribute on the element and
would run the resource selection algorithm as if it didn't exist. As long as
the encrypted content does not cause the selection algorithm to abort early in
existing browsers, I believe that adding this attribute to the
HTMLSourceElement is useful for applications that don't plan on using MSE.

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Received on Wednesday, 1 May 2013 14:07:32 UTC