AudioPassThroughUniversal

A command-line utility for macOS that captures audio from an aggregate device input and routes it to one or more output channel pairs using CoreAudio and AudioUnit.

Features

• Select an Aggregate Device (created in Audio MIDI Setup) that combines one or more physical input/output devices.
• Route any combination of source channels to any number of destination channels, including duplication and round-robin mapping.
• Minimal dependencies (only Swift, CoreAudio, AudioUnit).
• Optional debug logging controlled by a DEBUG flag in the source.

Requirements

• macOS 12.0 or later
• Swift 5.x toolchain
• Xcode command line tools (for swiftc)

Building

Compile the program as a universal binary (Intel + ARM) via the provided build script:

chmod +x build.sh
./build.sh

Or build manually with Swift:

swiftc -o AudioPassThroughUniversal AudioPassThrough.swift

Usage

./AudioPassThroughUniversal <AggregateDeviceName> <SrcChannels> <DstChannels>

• <AggregateDeviceName>: Name of the aggregate device (see Help below).
• <SrcChannels>: String of source channel numbers (e.g. 12 for channels 1 & 2).
• <DstChannels>: String of destination channel numbers (e.g. 3456 for channels 3, 4, 5 & 6).

Help

./AudioPassThroughUniversal -h

Displays usage and lists available Aggregate Devices on the system.

Examples

• Basic stereo pass-through (channels 1→3, 2→4):

  ./AudioPassThroughUniversal "MyAggregate" 12 34

• Duplicate stereo to two pairs (1→3,2→4 and 1→5,2→6):

  ./AudioPassThroughUniversal "MyAggregate" 12 3456

• Debug mode (enable by setting DEBUG = true in the source and recompiling):

  DEBUG=true ./AudioPassThroughUniversal "MyAggregate" 12 34

Additional CLI Tools

create-agg

A command-line utility to create an Aggregate Audio Device from two existing devices.

Usage:

./create-agg <AggDeviceName> <InputDeviceName> <OutputDeviceName>

• <AggDeviceName>: Desired name for the new aggregate device.
• <InputDeviceName>: Display name of the device to use as the master (input) device.
• <OutputDeviceName>: Display name of the device to include as the second device.

After running, the new aggregate device will be created and ready to use.

create-multi

A command-line utility to create a Multi-Output Audio Device (Stacked) from two or more existing devices.

Usage:

./create-multi <MultiDeviceName> <OutputDevice1> [OutputDevice2] [...]

• <MultiDeviceName>: Desired name for the new multi-output device.
• <OutputDevice1>, <OutputDevice2>, …: Display names of the devices to combine.

After running, the new multi-output device will be created and visible in Audio MIDI Setup as a stacked (multi-output) device.

Aggregate Device Setup

1. Open Audio MIDI Setup (macOS Utilities folder).
2. Click the + button under Audio Devices and choose Create Aggregate Device.
3. Add your input (e.g. BlackHoleA) and output (e.g. External Headphones) devices.
4. Rename the aggregate device to your desired <AggregateDeviceName>.

License

MIT License. See LICENSE for details.