Scream for macOS

Send your Mac's sound to speakers anywhere on your local network, with very low delay.

Scream for macOS adds a Scream Audio output device to your Mac. Pick it like any other output and everything you play is streamed to Scream receivers on your LAN: a Linux box with PulseAudio/PipeWire/ALSA/JACK, a Windows PC, an ESP32 speaker, and so on. It speaks the same protocol as the original Scream Windows driver, so every existing Scream receiver works unchanged.

• Native on Apple Silicon and Intel, macOS 13 or newer.
• No kernel extension and no security settings to change: Scream Audio is a user-space Core Audio driver.
• Volume keys and mute work. Settings survive reboots.
• Starts with your Mac and stays out of the way in the menu bar.

Install

1. Download Scream-x.y.z.pkg from the latest release.
2. Double-click it. The package is not notarized by Apple yet, so the first time macOS says it "cannot verify" it. Open System Settings > Privacy & Security, scroll down, click Open Anyway next to the Scream message, and open the package again.
3. Follow the installer. Sound pauses for a second while Core Audio reloads.

When the installer finishes, the Scream icon (radio waves) appears in the menu bar, your output switches to Scream Audio, and Scream is set to open at login. Start a receiver on your network and play something.

Using it

Click the radio-waves icon in the menu bar:

Menu item	What it does
Stream to Network (⌘S)	Switches the Mac's output to Scream Audio, or back to the speakers or headphones you used before. The icon is dimmed while not streaming.
Receiver	All Receivers (multicast, the default) or one receiver by IP address. Recent addresses are remembered.
Latency	Packet size. Lowest (1.5 ms at 48 kHz) has the least delay; Standard (6 ms) works with every receiver.
Quality	16, 24 or 32 bit; 44.1, 48, 88.2 or 96 kHz. 48 kHz / 16 bit is plenty for most setups. The Format menu for Scream Audio in Audio MIDI Setup changes the same setting.
Open at Login	Start Scream with your Mac (on by default).
Uninstall Scream…	Removes everything, see below.

You can also pick Scream Audio directly in System Settings > Sound, in Control Center, or in any app's output menu, just like AirPlay or USB speakers. The same settings are available in Terminal through screamctl (screamctl -h).

Setting up a receiver

On Linux, build the receiver from Receivers/unix and run it:

scream -o pulse              # PulseAudio / PipeWire, multicast
scream -o alsa               # plain ALSA
scream -u -o pulse           # unicast: then choose this machine's IP in Receiver

If the receiver has a firewall, open UDP port 4010. Other receivers: Windows ScreamReader, Android (Receivers/android), and third-party ones such as ESP32 and STM32 speakers, cornrow and freeRtr.

Getting the lowest delay

The Mac sends every audio buffer the moment Core Audio hands it over, so most of the delay you hear is the receiver's buffer.

• Lower the receiver's buffer: scream -o pulse -t 10 (the default is 50 ms). If you hear dropouts, go up to 20.
• Choose Latency > Lowest in the menu. The Linux receiver supports it; if another receiver goes silent, use Standard.
• Use wired Ethernet if you can. On Wi-Fi, prefer a specific receiver over All Receivers: many access points send multicast slowly and drop it.

Uninstall

Choose Uninstall Scream… in the menu and enter your password. If you already dragged Scream to the Trash, run this in Terminal instead:

sudo scream-uninstall

Both remove the app, the Scream Audio device and the command line tools, and your Mac switches back to its own speakers.

Building from source

cd Senders/macos
make            # driver, menu bar app, screamctl
make pkg        # build/Scream-<version>.pkg
sudo make install

You need the Xcode Command Line Tools (xcode-select --install). See Senders/macos/README.md for how the driver works, and the GitHub Actions workflow that builds, installs and stream-tests every change on a real Mac. Pushing a v* tag publishes the installer as a release.

Protocol

Audio goes out as UDP to multicast 239.255.77.77:4010 (or to one unicast address). Each packet has a 5 byte header followed by up to 1152 bytes of little-endian PCM:

Byte	Meaning
0	Sample rate. Bit 7 selects the base, 0 = 48 kHz, 1 = 44.1 kHz; the other bits are the multiplier.
1	Sample width in bits (16, 24, 32).
2	Number of channels.
3-4	Channel mask (dwChannelMask of WAVEFORMATEXTENSIBLE), little-endian.

A Wireshark dissector lives in tools/wireshark.

About this fork

This is a fork of duncanthrax/scream by Tom Kistner and contributors, which provides the Windows driver and the receivers. Everything macOS-specific is in Senders/macos. The Windows driver source is still here, unchanged; its documentation is in doc/WINDOWS.md.

Licensed under MS-PL, like the original. See LICENSE.