Prism – macOS Virtual Audio Splitter

Prism is a virtual audio splitter for macOS. It exposes a 64-channel bus where every app can be pinned to its own stereo pair, so you can feed OBS, DAWs, and recorders with isolated tracks while preserving a separate monitor mix. The driver is written in Rust and uses Accelerate (vDSP) for its realtime mixing path.

Ecosystem

Prism is part of a two-app audio workflow:

• Prism (this driver + CLI): Splits application audio → assigns each app to virtual device channels
• Spectrum: Takes those channels → mixes and routes to physical output devices

Highlights

• Per-application routing – send each process to its own stereo pair on the 64-channel bus.
• Separable stems – capture game audio, voice chat, music, and system alerts on independent channels for streaming or editing.
• Instant muting on reroute – Prism clears a slot the moment an app disconnects or moves, so recordings never pick up stale audio.
• Automation-ready – drive routing changes via the prism CLI or by scripting its Unix socket API.

Use cases

• Streaming with OBS/Streamlabs – capture the game, voice chat, and music on isolated inputs so the mixer scene stays tidy.
• Multitrack podcasting or post-production – record each participant or app feed to its own track inside Logic, Reaper, or Audition.
• Hybrid events – send different mixes to Zoom, in-room PA, and a backup recorder without touching physical patch bays.
• Creative monitoring – audition reference audio or click tracks privately while the audience hears only the main program.

Prerequisites

• macOS 13 or later.
• Xcode Command Line Tools (xcode-select --install).
• Rust toolchain (rustup), using the default stable channel.

Build and Install

1. Install the CLI and daemon

cargo install --path .

cargo install places prism and prismd under ~/.cargo/bin/; ensure that directory is on your PATH.

2. Build the CoreAudio driver bundle

./build_driver.sh

This script compiles the plugin binary, updates the bundle under Prism.driver/, and performs codesign stubs if required.

3. Install the driver

sudo ./install.sh

The installer copies Prism.driver into /Library/Audio/Plug-Ins/HAL/ and refreshes permissions.

4. Reboot

Reboot macOS to allow the HAL plug-in to load.

Usage

1. Launch the daemon

prismd --daemonize

The --daemonize flag double-forks and detaches prismd. Omit it if you prefer to run in the foreground for logging.

2. Manage routing with the CLI

# List all currently attached clients and their channel offsets
prism clients

# Route PID 12345 to the stereo slot that starts at channel offset 4
prism set 12345 4

# Route an app by bundle display name without hunting for its PID
prism set-app "Google Chrome" 3-4

Routing requests are serialized as a custom 'rout' property containing { pid: i32, channel_offset: u32 }. The driver consumes the property, updates the slot table, and clears the corresponding loopback pair if the client moved.

prism set-app uses process metadata to find the most recently active instance of the named app (partial matches allowed) and pins it to the requested stereo pair, making quick reroutes during a stream much easier than tracking PIDs.

Use prism --help to discover additional subcommands.

Mixing model

• Channels 1/2 always carry the same full-system mix you hear through your speakers.
• Every pinned app gets its own stereo pair on the 64-channel bus, so you can record or stream it separately.
• Reroute apps on the fly without pops or stale audio—the mix updates instantly every cycle.
• Tuned for live workflows, keeping latency low even when lots of apps are active.
• Apple’s Accelerate framework (vDSP) handles the math under the hood, keeping CPU use light.

Uninstall

1. Remove the CLI and daemon binaries (optional):

cargo uninstall prism

2. Remove the driver bundle:

sudo ./uninstall.sh

3. Reboot to unload the HAL plug-in.

License

MIT License. See LICENSE for details.