I wrote the MuteTab Chrome extension (http://www.mutetab.com/) and have been following the development of this feature in Chrome's bug tracker.
The reason this feature hasn't existed is that Chrome (like all browsers other than IE) would use just a single instance of Flash for all tabs so the browser could not control the volumes independently nor tell which Flash instances were playing sound or might ever play sound. You can read this explanation from Chrome devs here: http://www.reddit.com/r/IAmA/comments/gdyun/iama_we_are_thre...
My understanding (just from reading comments in the bug tracker) is that Google was able to get Adobe to cooperate with them and add some hooks so they could keep track of the sounds for each Flash plug-in separately.
I was able to try this feature out in today's Canary build and it worked for me on the two sites I tried it on: youtubedoubler.com and homestarrunner.com.
The URL chrome://media-internals is also interesting in that it will show an entry for each plug-in instance browser-wide. Hopefully they will have a UI element similar to this or like MuteTab so that a person can find the tab making sound when they have a huge number of tabs open in multiple windows and cannot see all of the audio indicators.
This is one of the benefits of our work to sandbox Flash. In order to support the sandbox we had to broker out all IO and system access by porting to PPAPI. So, this means that everything goes through Chrome's stack and we can control it much like web content content. Unfortunately, this doesn't work for NPAPI plugins since they don't go through Chrome's stack.
The reason this feature hasn't existed is that Chrome (like all browsers other than IE) would use just a single instance of Flash for all tabs so the browser could not control the volumes independently nor tell which Flash instances were playing sound or might ever play sound. You can read this explanation from Chrome devs here: http://www.reddit.com/r/IAmA/comments/gdyun/iama_we_are_thre...
My understanding (just from reading comments in the bug tracker) is that Google was able to get Adobe to cooperate with them and add some hooks so they could keep track of the sounds for each Flash plug-in separately.
I was able to try this feature out in today's Canary build and it worked for me on the two sites I tried it on: youtubedoubler.com and homestarrunner.com.
The URL chrome://media-internals is also interesting in that it will show an entry for each plug-in instance browser-wide. Hopefully they will have a UI element similar to this or like MuteTab so that a person can find the tab making sound when they have a huge number of tabs open in multiple windows and cannot see all of the audio indicators.