> This document extends the Web platform with the ability to direct audio output to non-default devices, when authorization is given. Authorization is necessary because playing audio out of a non-default device may be unexpected behavior to the user, and may cause a nuisance. For example, suppose a user is in a library or other quiet public place where she is using a laptop with system audio directed to a USB headset. Her expectation is that the laptop’s audio is private and she will not disturb others. If any Web application can direct audio output through arbitrary output devices, a mischievous website may play loud audio out of the laptop’s external speakers without the user’s consent.

> To prevent these kinds of nuisance scenarios, the user agent must acquire the user’s consent to access non-default audio output devices. This would prevent the library example outlined earlier, because the application would not be authorized to play out audio from the system speakers.

> The default audio output device is always authorized.

:-(

    [1] http://www.w3.org/TR/audio-output/#privacy-consent (section 5.1)

My thought exactly when the music started playing. But I think this could better be implemented in the browser/ via an extension. You can't trust users to follow a convention all the time.

EDIT: Someone found my comment worth downvoting.