Soundfork
macOS · 2026
A macOS menu-bar app that separates audio across multiple outputs, one app on a Bluetooth speaker, another on the Mac's own speakers, each with its own volume, instead of everything sharing one output.
- Role
- Solo developer
- Impact
- Per-app audio routing on macOS without installing a driver
Challenge
On my Android phone I can play music on a speaker and still watch something on the phone itself. macOS sends every app to the same output, so I couldn't do that on my Mac. I wanted Spotify on a Bluetooth speaker while a video played through the laptop, each at its own volume.
Contribution
I built the whole app in Swift and SwiftUI: the Core Audio routing, the panel that drops out of the notch, and the logic that remembers each app's route and falls back when a speaker disconnects. I also wrote the release script and the CI that runs the tests on every push.
Outcome
It's released on GitHub as a universal build for Apple Silicon and Intel Macs. Because it only uses public process taps, quitting or crashing never leaves an app muted; the taps go away with it.
Details
I built Soundfork because macOS only gives you one audio output for everything. I wanted to split sound across multiple outputs at once, one source on a Bluetooth speaker, another on the Mac's own speakers, so I built the per-app version myself.
It uses Core Audio's process taps, the same public API screen recorders use, to capture one app's audio and send it to any device, with its own volume, independent of everything else. No kernel extension, no virtual driver. Under the hood that's a private aggregate device combining the tap and the destination on one clock, and a real-time callback copying and ramping the gain, lock-free since it runs on Core Audio's real-time thread.
It lives in the notch as a dynamic-island-style panel, remembers every app's route across restarts, and falls back cleanly if a Bluetooth speaker drops mid-song. Shipped as a signed DMG with CI running the full test suite on every push.
Stack
Swift · SwiftUI · Core Audio · macOS