loopback

Creates a virtual stereo input device that captures all system audio output, making it available to macOS screen recording — no Audio Server Plugin installation required.

Why

macOS screen recording captures from input devices, not output devices. loopback bridges that gap by tapping all system audio output and re-presenting it as a named stereo input device.

Requirements

• macOS 14.2+
• Rust toolchain

Usage

Install with make install, then run by name:

loopback

Or run directly from the project without installing:

cargo run

The device becomes available system-wide while the process is running. Ctrl+C removes it. The default device name is loopback. Run with --help to print help message.

Screen recording

1. Start loopback
2. Open the screen recording picker (Cmd+Shift+5)
3. Select the device name from "Use audio from"
4. Record — audio will be a stereo mix of all system audio output

How it works

Uses two macOS APIs:

• AudioHardwareCreateProcessTap (macOS 14.2+) — global stereo tap that captures all process audio system-wide, regardless of which output device or channel each process uses
• AudioHardwareCreateAggregateDevice — wraps the tap in a public aggregate device so screen recording can enumerate and select it by name

The tap is CATapUnmuted, so the source audio continues playing normally.