[webkit-gtk] Question about Media Source Extension

[Michael Catanzaro]

On Wed, Feb 28, 2018 at 1:20 AM, Cédric Bellegarde 
<cedric.bellegarde at adishatz.org> wrote:
> And here my surprise, with -DENABLE_MEDIA_SOURCE=ON and 
> enable-mediasource=False, 1080p is available in YouTube and WebKitGTK 
> does not crash anymore.

WOW! This is a major discovery.

The good news is that you must have been testing our stable release 
rather than  our latest development release, WebKitGTK+ 2.19.91, where 
we actually have enabled the ENABLE_MEDIA_SOURCE=ON build option. It's 
still off by default at runtime, because it does not work reliably yet, 
but that is exactly the configuration that you've requested.

It seems quite bad that enabling the build option but not the runtime 
option enables higher-resolution video playback on YouTube, though, 
because that means that the feature is somehow web-exposed such that 
YouTube can detect it, even though it is supposed to be disabled at 
runtime. That seems like a major bug. It indicates that the runtime 
option does not function properly in some way or another, and that 
leaving the build option enabled is risky, and that we should 
reevaluate our choice to enable the build option. This is somewhat 
urgent, because we have a new stable release coming up in a week and a 
half. Enrique, Alicia, could you investigate this to see what is wrong, 
please?

In the past, when the MSE feature was originally developed, WebKit did 
not support hiding JavaScript features at runtime. That's no longer the 
case -- nowadays, we would expect the MSE features to be completely 
invisible to webpages when the runtime option is disabled -- but 
perhaps that was never properly implemented for MSE. (That is actually 
the reason why we have started using more runtime options in WebKit, in 
preference to build options.) Anyway, I don't know how to fix this; it 
requires some investigation.

Michael