Project · Fader
One Mac, every app on its own fader.
Fader is a menu-bar mixer for macOS. Each app that is playing gets its own volume, mute, and output device, so Spotify can stay on your headphones while the browser plays through the speakers.
Role
Product design, Swift, Core Audio
Stack
Swift · SwiftUI · Core Audio process taps
Platform
macOS 14.2 and later
Status
Open source · MIT
macOS gives you one volume and one output. Most days need more than that.
Music, calls, and videos all fight over the same slider. Fader captures each app with a Core Audio process tap, applies that app's volume, and plays it on the device you pick. Quit it and audio goes back to the system output.
Only what's playing
The panel lists apps that are making sound right now, and holds a row for a couple of seconds between tracks so it doesn't flicker.
Remembers you
Each app's volume, mute, and device are saved. New apps follow the system output until you choose otherwise.
Handles unplugging
Pull your headphones and that app falls back to the system output, then returns to them when they reconnect.
Logic you can test
Routing rules, app grouping, and saved settings live in a separate core module with unit tests that run without Core Audio.