Current Google Chrome version 45 automatically shows an audio indicator for music playing tabs, Chrome does allow you to mute a tab by clicking on the icon (in fact, multiple number of tabs), you need to enable chrome://flags/#enable-tab-audio-muting flag for that.
Keyboard Shortcuts to Mute Tabs in Chrome
Mute tab keyboard shortcut: The default keyboard shortcut, with which you can mute a tab without relation to flag is Alt+M, this works in Firefox also.
Muting multiple tabs: Hold down the ‘Ctrl’ key and select the tabs that you want to mute, right click on the tab context menu and select ‘mute tabs’. That works and working now.
If you want to customize these shortcuts, install Mute Tab shortcuts extension in the browser and use the below shortcuts or customize them according to your liking by visiting Chrome:/extensions page and by selecting ‘keyboard shortcuts’ option.
Mute current tab – Alt + Shift + M
Mute all tabs – Alt + Shift + Comma
Unmute all tabs – Alt + Shift + Period
The default shortcuts which Chrome, extension and you create, all will work when they’re different.
Note: The flag we mentioned in the article may not last long it will be removed by Google once they enable the feature.