Project 3: User-Space Sound Server (Mini PipeWire)

A daemon that sits between applications and ALSA, allowing multiple apps to play audio simultaneously with mixing.

Quick Reference

Attribute Value
Primary Language See main guide
Alternative Languages N/A
Difficulty See main guide
Time Estimate See main guide
Knowledge Area See main guide
Tooling See main guide
Prerequisites C programming, IPC mechanisms, completed Project 1

What You Will Build

A daemon that sits between applications and ALSA, allowing multiple apps to play audio simultaneously with mixing.

Why It Matters

This project builds core skills that appear repeatedly in real-world systems and tooling.

Core Challenges

  • Creating a Unix domain socket server for client connections
  • Implementing a shared memory ring buffer protocol
  • Real-time mixing of multiple audio streams
  • Sample rate conversion when clients use different rates
  • Latency management and buffer synchronization

Key Concepts

  • Map the project to core concepts before you code.

Real-World Outcome

# Start your sound server (replacing PulseAudio/PipeWire for testing)
$ ./my_sound_server --device hw:0,0 --format S16_LE --rate 48000

╔═══════════════════════════════════════════════════════════════════╗
║                    My Sound Server v1.0                            ║
║                    PID: 12345                                      ║
╠═══════════════════════════════════════════════════════════════════╣
║ Output Device: hw:0,0 (HDA Intel PCH)                              ║
║ Format: S16_LE @ 48000 Hz, Stereo                                  ║
║ Buffer: 2048 frames (42.67 ms) | Period: 512 frames (10.67 ms)     ║
║ Latency target: 20 ms                                              ║
╠═══════════════════════════════════════════════════════════════════╣
║ Socket: /tmp/my_sound_server.sock                                  ║
║ Status: Listening for clients...                                   ║
╚═══════════════════════════════════════════════════════════════════╝

Implementation Guide

  1. Reproduce the simplest happy-path scenario.
  2. Build the smallest working version of the core feature.
  3. Add input validation and error handling.
  4. Add instrumentation/logging to confirm behavior.
  5. Refactor into clean modules with tests.

Milestones

  • Milestone 1: Minimal working program that runs end-to-end.
  • Milestone 2: Correct outputs for typical inputs.
  • Milestone 3: Robust handling of edge cases.
  • Milestone 4: Clean structure and documented usage.

Validation Checklist

  • Output matches the real-world outcome example
  • Handles invalid inputs safely
  • Provides clear errors and exit codes
  • Repeatable results across runs

References

  • Main guide: AUDIO_SOUND_DEVICES_OS_LEARNING_PROJECTS.md
  • Primary references are listed in the main guide