README
¶
ZuidWest FM Encoder
Audio streaming software for ZuidWest FM and Radio Rucphen. Stream audio from a Raspberry Pi to multiple SRT destinations simultaneously. Built for broadcast environments with real-time monitoring and web-based configuration.
Features
- Multi-output streaming - Send to multiple SRT servers with different codecs simultaneously
- Real-time VU meters - Peak hold (1.5s) with Peak/RMS toggle, updated via WebSocket
- Silence detection - Alerts via webhook or email when audio drops below threshold
- Web interface - Configure outputs, select audio input, monitor levels
- Auto-recovery - Automatic reconnection with exponential backoff
- Multiple codecs - MP3, MP2, OGG Vorbis, or uncompressed WAV per output
- Single binary - Web interface embedded, minimal runtime dependencies
Requirements
- Raspberry Pi 4 or 5
- HiFiBerry Digi+ I/O or HiFiBerry DAC+ ADC
- Raspberry Pi OS Trixie Lite (64-bit)
- FFmpeg (for encoding)
- alsa-utils (for audio capture via arecord)
Installation
- Install Raspberry Pi OS Trixie Lite (64-bit)
- Configure HiFiBerry following the official guide
- Run the installer as root:
sudo su
/bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/oszuidwest/zwfm-encoder/main/deploy/install.sh)"
The web interface will be available at http://<raspberry-pi-ip>:8080
Default credentials: admin / encoder
Audio Input
Connect the digital output of your audio processor to the HiFiBerry input.
Requirements:
- 48 kHz sample rate
- 16-bit depth
- SPDIF format preferred (AES/EBU may work but is not guaranteed)
Codecs
| Codec | Encoder | Bitrate |
|---|---|---|
| MP3 | libmp3lame | 320 kbit/s |
| MP2 | libtwolame | 384 kbit/s |
| OGG | libvorbis | ~500 kbit/s (Q10) |
| WAV | pcm_s16le | Uncompressed |
Silence Detection
Monitors audio levels and sends alerts when silence is detected. Uses hysteresis to prevent alert flapping:
| Setting | Default | Range | Description |
|---|---|---|---|
| Threshold | -40 dB | -60 to 0 | Audio level below which silence is detected |
| Duration | 15 s | 1-300 | Seconds of silence before alerting |
| Recovery | 5 s | 1-60 | Seconds of audio before considering recovered |
Alerting options:
- Webhook - POST request to a URL when silence starts
- Email - SMTP notification to configured recipients
Configure via the web interface under Settings → Alerts.
Configuration
Configuration is stored in config.json:
{
"web_port": 8080,
"web_user": "admin",
"web_password": "encoder",
"audio_input": "default:CARD=sndrpihifiberry",
"silence_threshold": -40,
"silence_duration": 15,
"silence_recovery": 5,
"silence_webhook": "https://example.com/alert",
"outputs": [
{
"id": "output-1",
"host": "srt.example.com",
"port": 9000,
"streamid": "studio",
"password": "secret",
"codec": "mp3",
"enabled": true
}
]
}
Architecture
flowchart LR
subgraph Input
A[Audio Source<br>S/PDIF]
end
subgraph Capture
B[arecord<br>Raw PCM]
end
subgraph Distribution
C[Go Distributor<br>+ Level Metering]
end
subgraph Encoding
D1[FFmpeg MP3]
D2[FFmpeg MP2]
D3[FFmpeg OGG]
end
subgraph Output
E1[SRT Server 1]
E2[SRT Server 2]
E3[SRT Server 3]
end
A --> B --> C
C --> D1 --> E1
C --> D2 --> E2
C --> D3 --> E3
On Linux, arecord captures audio from ALSA with minimal CPU overhead. The Go distributor calculates RMS/peak audio levels directly from the PCM stream and fans out the audio to multiple FFmpeg encoder processes. Each encoder streams to its own SRT destination.
On macOS (for development), FFmpeg with AVFoundation is used for capture instead of arecord.
Post-installation
Optional cleanup to reduce attack surface:
# Disable WiFi
echo "dtoverlay=disable-wifi" >> /boot/firmware/config.txt
# Remove unnecessary packages
apt remove bolt bluez ntfs-3g rsyslog telnet
SRT Resources
Related
- Liquidsoap Server - Companion server software for receiving SRT streams
License
MIT License - See LICENSE.md
Documentation
¶
Overview ¶
Package main implements an audio streaming encoder that captures audio from digital input and streams to multiple SRT destinations.
Usage:
encoder [-config path/to/config.json]
If -config is not specified, the encoder looks for config.json in the same directory as the binary.
Source Files
Directories
¶
| Path | Synopsis |
|---|---|
|
internal
|
|
|
audio
Package audio provides audio processing utilities including level metering and silence detection.
|
Package audio provides audio processing utilities including level metering and silence detection. |
|
config
Package config provides application configuration management.
|
Package config provides application configuration management. |
|
encoder
Package encoder provides the audio capture and encoding engine.
|
Package encoder provides the audio capture and encoding engine. |
|
notify
Package notify provides notification services for silence alerts.
|
Package notify provides notification services for silence alerts. |
|
output
Package output manages FFmpeg output processes for streaming.
|
Package output manages FFmpeg output processes for streaming. |
|
server
Package server provides the HTTP server and WebSocket handler for the web interface.
|
Package server provides the HTTP server and WebSocket handler for the web interface. |
|
types
Package types provides shared type definitions used across the encoder.
|
Package types provides shared type definitions used across the encoder. |