You cannot do it now, although this hopefully will change in the near future.
There is currently nothing in the Chrome API, although in February I proposed the tabaudio API (and now I'm working on a new project, as well as an implementation).
Can you give me an idea of ββwhy you want this functionality? (They are asking for potential use in developing APIs.)
Perhaps the closest you can do is something similar to what the MuteTab Chrome extension (written by me, http://www.github.com/jaredsohn/mutetab ) does, which basically crawls the page for objects, paste, audio, video and applet tags and hides them from the page. Unfortunately, this skips web audio. In addition, instead of turning it off, it βstopsβ it by removing it from the page, which can block a video or game related to sound. Also, if you just like HTML5 video or audio with Flash with an API (like YouTube), you can use JavaScript to pause or mute the sound.
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