How to set a different volume for each app on a Mac

You want a video quieter while your music stays where it is. macOS has one output volume shared by every app, so the volume keys move everything together. There are three ways around it.

The short version

Use the app's own volume slider, if it has one.
In Safari, mute one noisy tab.
For a real slider per app, use a per-app volume mixer in the menu bar.

1. Use each app's own slider

Spotify, Music, Zoom, Discord and the YouTube player each have a volume slider inside the app. Turn one of them down and the others stay as they are.

The catch: every app keeps its slider in a different place, and some have none. Safari, for example, has no volume control of its own: only the player inside the web page does.

2. Mute a single Safari tab

When a tab plays sound, Safari shows a speaker icon on that tab and in the address field. Click it to mute that tab. That works for silencing an autoplaying video, but it is only on or off: you cannot make the tab half as loud.

3. Use a per-app volume mixer

A mixer app gives every app that plays sound its own slider, in one place. calmdoo lives in the menu bar: click the speaker icon and each playing app has a row. Drag Safari to 40%, leave Spotify at 100%, mute Chrome. calmdoo remembers each app's setting for next time.

Below 100% and above. The middle of each slider is 100%. Left is quieter, right boosts up to 400%.
An EQ and a compressor per app. More bass for music, clearer voices for calls, steadier dialogue in films.
No driver. calmdoo uses the audio taps built into macOS, so nothing is installed into the system. If it quits, every app plays at its normal volume again.

Other mixers exist, some with features calmdoo does not have, like sending apps to different speakers. See volume apps for Mac compared.

calmdoo does this from your menu bar

A slider for every app that plays sound, boost up to 400% with a limiter, and an EQ and compressor per app. Open source, no driver, no account. macOS 15 or later.