When the user presses one of the three volume-related keys (Mute, Volume Down, or Volume Up), a bubble appears in the lower-right corner of the screen displaying the current volume level.
Non-muted and ~60% of maximum level
At the left, an icon shows whether the system is muted or not, and if not muted, a coarse approximation of the current volume level (via zero, one, or two sound waves emanating from a speaker). To the right of the icon, a toggle button displays the current muting status.
Muted with ~60% level saved
Either the icon or the toggle button can be clicked to toggle the muting status. At the right side of the bubble, a horizontal slider displays the current volume level. If the system is muted, the slider is displayed in an inactive state; note that the previously-set volume level is still visible, though.
The same controls are present in the larger bubble that is displayed when the user clicks the system / status tray in the lower-right corner of the screen:
The volume keys’ current behavior was initially proposed in chromium-os bug 13618. Briefly,
Mute: mutes instantly
Volume Down: decreases the volume
Volume Up: increases the volume
Mute: does nothing
Volume Down: sets the saved volume to zero, keeping the system muted
Volume Up: unmutes and restores saved volume (increasing it slightly if zero)
When in an environment where sound is undesirable (e.g. library, shared office, etc.), the user is guaranteed that pressing the Mute key will instantly mute the system; there is no risk of toggling sound back on if the system was already muted. If the user wants to set the volume to the lowest audible level, only three key-presses are needed (Mute, Volume Down, and then Volume Up).
This is a poor substitute; decreasing the volume from 100% to 0% takes more than a second and the user is unable to easily restore the original volume level later.
The toggle button between the icon and the slider is confusing (see e.g. this bug).The button was originally labeled, but the label’s visual appearance was sub-optimal (chromium bug 143426). Per chromium bug 152070, the unlabeled button will be merged into a more-meaningful icon (as tracked in chromium bug 137947).