The desktop tray application captures system or per-application audio. Each connected phone has independent source, bitrate, and playback-buffer settings. Phones selecting the same source share capture, with separate encoders.

Platforms

Platform	Audio implementation
Windows	WASAPI desktop and per-process capture; cpal desktop fallback
Linux	PipeWire desktop and per-process capture; cpal desktop fallback
macOS 13+	ScreenCaptureKit desktop and per-process capture; cpal desktop fallback
macOS 11–12	cpal desktop capture; no per-process capture
Android 8.0+ (API 26)	Native playback through Oboe

The macOS cpal path requires system audio routed to a capture device. ScreenCaptureKit requires Screen Recording permission. iOS is not implemented.

Installation

Packages are available on the release page.

Platform	Package
Windows	.msi installer or .zip archive
Linux	.deb, .rpm, .AppImage, or .tar.xz
macOS	.dmg
Android ARM64	gemacast-mobile.apk
Android, multiple architectures	gemacast-mobile-universal.apk

Linux package installation:

sudo apt install ./gemacast-pc_*.deb       # Debian / Ubuntu
sudo dnf install ./gemacast-pc-*.rpm      # Fedora

Linux archives require GTK3 and AppIndicator runtime libraries for the tray. The Windows MSI installs firewall exceptions. Linux package scripts attempt firewall configuration; portable archives and AppImages do not.

The macOS application is unsigned and unnotarized. To remove quarantine after copying it into Applications:

xattr -d com.apple.quarantine /Applications/Gemacast.app

Connection

1. Start the PC tray application and the Android application.
2. Configure a connection mode from the table below and select the PC on the phone.
3. During initial pairing, compare the six-digit code on both devices and approve.
4. Select desktop or application audio and start playback.

Mode	Setup	Transport
Wi-Fi	Connect both devices to the same reachable LAN	UDP audio; HTTPS/WSS control
USB tethering	Connect USB and enable Android USB tethering	Same protocol as Wi-Fi over the tethered interface
ADB	Enable USB debugging, connect USB, and approve the computer	TCP connections through automatic adb reverse

LAN discovery can be blocked by client isolation, guest networks, VPN routing, or firewall rules. ADB discovery uses the forwarded connection.

Audio

All sources are converted to 48 kHz stereo. Each 10 ms frame contains 480 samples per channel, or 960 interleaved samples.

Format	Encoding	Audio payload rate
Opus	LowDelay/CELT	6–512 kbit/s
PCM	Native-endian f32 stereo	3.072 Mbit/s, excluding transport overhead

Playback provides adaptive and fixed jitter-buffer presets, gain control, optional PC-volume matching, and automatic reconnection. Each phone buffers independently; playback is not synchronized across phones.

The displayed RTT and buffer depth do not measure capture-to-speaker latency. Capture, encoding, network transport, decoding, and output buffers also contribute to that delay.

Authentication and privacy

• Control uses TLS and P-256 device authentication. Pairing compares a six-digit code; approved PC identities are stored on the phone.
• Session tokens are memory-only and rotate on connection. A changed PC certificate requires forgetting its stored identity before pairing again.
• UDP audio is neither encrypted nor authenticated. LAN streaming therefore requires a trusted network.
• An authenticated phone can request the PC process list to select an audio source.
• ADB audio passes through the approved debugging connection and has no separate audio encryption.

Network ports

Port	Protocol	Use
23555	UDP	LAN discovery and probes
23556	UDP	Audio received by the phone
23559	TCP	HTTPS/WSS control received by the PC

The PC sends audio from an ephemeral UDP port. The phone returns heartbeat and RTT traffic to that sender port. Firewalls must allow the audio flow and replies. ADB forwards TCP 23557 (audio), 23558 (discovery), and 23559 (control); it needs no LAN firewall rule.

The Linux firewalld service includes UDP 23555–23556 and TCP 23559. Equivalent UFW rules:

sudo ufw allow 23555,23556/udp
sudo ufw allow 23559/tcp

Interface

Application selection, settings, and desktop tray

Documentation

Document	Content
Architecture	Components, session lifecycle, transport, and packet formats
Contributing	Setup, builds, checks, diagnostics, and issue/PR contents
Development constraints	Repository-specific coding constraints
Website	Vue source map and commands
Containers	Linux and Android check environments

License

GPL-3.0-or-later. Third-party dependencies are listed in THIRD_PARTY_NOTICES.md.