The Unwanted Audio Swap
AirPlay is Apple’s proprietary wireless streaming protocol. In recent versions of macOS, Apple has aggressively tried to make the transition between devices seamless. If you have an AirPlay-compatible speaker (like a HomePod or a Sonos system) on the same Wi-Fi network, macOS might automatically attempt to route your system audio to that device if it detects you are playing media and the speaker is nearby and idle. This “handoff” feature can lead to incredibly embarrassing or frustrating situations where you start playing a video on your MacBook in your office, only to realize the audio is blaring at full volume in the living room.
Isolating Your System Audio
To guarantee that your audio always plays locally through your Mac’s speakers or connected headphones, and to stop macOS from automatically pushing sound to network AirPlay devices, you must disable the Handoff configuration.
Click the Apple logo in the top-left corner of your screen and select System Settings. Scroll down the left-hand navigation pane and click on General. In the right-hand panel, click on AirDrop & Handoff. Look down the list of options until you find the setting specifically related to audio routing. It is usually labelled Automatically AirPlay to TVs and speakers. Click the dropdown menu next to this setting. By default, it is often set to “Automatic” or “Ask.” You must change this setting strictly to Never. Once changed, macOS will completely ignore the presence of nearby HomePods or AirPlay receivers unless you manually click the AirPlay icon in the menu bar and explicitly select a device.