# How Fastfetch Detects Sound Cards: A Deep Dive into Cross-Platform Audio Detection

> Learn how Fastfetch detects sound cards using native APIs like PulseAudio Core Audio MMDevice and OSS. Explore its cross-platform audio detection in this deep dive.

- Repository: [fastfetch-cli/fastfetch](https://github.com/fastfetch-cli/fastfetch)
- Tags: deep-dive
- Published: 2026-03-30

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**Fastfetch detects sound cards through a modular, platform-specific architecture that delegates to native audio APIs—PulseAudio on Linux, Core Audio on macOS, MMDevice on Windows, and OSS on BSD—unified under the `ffDetectSound()` interface in `src/detection/sound/`.**

Fastfetch is a high-performance system information tool written in C that aggregates hardware and software details across multiple operating systems. Its sound card detection mechanism exemplifies the project's portable design philosophy, abstracting OS-specific audio APIs into a uniform data model while maintaining zero runtime dependencies through dynamic library loading.

## The Architecture of Sound Detection in Fastfetch

The detection flow follows a layered architecture that separates the presentation module from platform-specific implementation details. When a user requests sound card information, the call chain originates in [`src/modules/sound/sound.c`](https://github.com/fastfetch-cli/fastfetch/blob/main/src/modules/sound/sound.c) where `ffPrintSound()` initializes a result list and invokes the detection engine.

```c
// src/modules/sound/sound.c
bool ffPrintSound(FFSoundOptions* options) {
    FF_LIST_AUTO_DESTROY result = ffListCreate(sizeof(FFSoundDevice));
    const char* error = ffDetectSound(&result);
    // Filtering and formatting logic follows...
}

```

The **public API `ffDetectSound()`** declared in [`src/detection/sound/sound.h`](https://github.com/fastfetch-cli/fastfetch/blob/main/src/detection/sound/sound.h) serves as a thin wrapper that forwards to the appropriate platform implementation selected at compile time via feature macros (e.g., `FF_HAVE_PULSE`, `FF_HAVE_COREAUDIO`). Each implementation populates a linked list of `FFSoundDevice` structures containing the device identifier, human-readable name, volume level, active state, and default device designation.

## Platform-Specific Detection Implementations

Fastfetch implements dedicated detection backends for each supported operating system, ensuring native performance without abstraction penalties.

### Linux PulseAudio Detection

On Linux systems, [`src/detection/sound/sound_linux.c`](https://github.com/fastfetch-cli/fastfetch/blob/main/src/detection/sound/sound_linux.c) implements **dynamic loading of libpulse** to avoid hard dependencies. The code initializes a PulseAudio main loop and queries the server using `pa_context_get_sink_info_list` to enumerate output devices and `pa_context_get_server_info` to identify the default sink.

The implementation extracts each sink's name, index, current volume (converted to percentage), and active state. The callback `paServerInfoCallback` marks the default sink with the `main` flag, enabling Fastfetch to distinguish between active outputs and the system default.

If PulseAudio support is disabled at compile time (`#ifndef FF_HAVE_PULSE`), the function returns `"Fastfetch was built without libpulse support"` rather than attempting detection.

### macOS and iOS Core Audio

The Apple implementation in [`src/detection/sound/sound_apple.c`](https://github.com/fastfetch-cli/fastfetch/blob/main/src/detection/sound/sound_apple.c) leverages the **CoreAudio framework** through `AudioObjectGetPropertyData`. It enumerates output devices using the `kAudioHardwarePropertyDevices` selector, then queries each device for its UID, name, and mute state.

Volume detection uses `kAudioDevicePropertyVolumeScalar` or per-channel volume properties when available. The implementation identifies the default output device via `kAudioHardwarePropertyDefaultOutputDevice` and marks it accordingly in the `main` field of the `FFSoundDevice` structure.

### Windows MMDevice API

Windows detection resides in [`src/detection/sound/sound_windows.cpp`](https://github.com/fastfetch-cli/fastfetch/blob/main/src/detection/sound/sound_windows.cpp) and utilizes the **COM-based MMDevice API**. The code initializes COM with `ffInitCom()`, creates an `IMMDeviceEnumerator`, and enumerates audio endpoints via `IMMDeviceCollection`.

For each endpoint, Fastfetch retrieves the friendly name through `IPropertyStore`, volume and mute states through `IAudioEndpointVolume`, and marks the default endpoint (obtained via `GetDefaultAudioEndpoint`) as the main device. This approach supports both playback and recording devices while handling the Windows audio subsystem's session-based architecture.

### BSD OSS Interface

The BSD implementation in [`src/detection/sound/sound_bsd.c`](https://github.com/fastfetch-cli/fastfetch/blob/main/src/detection/sound/sound_bsd.c) interfaces with the **OSS (Open Sound System)** through `/dev/mixer*` device nodes. It queries system information using `SNDCTL_SYSINFO`, reads device capabilities with `SOUND_MIXER_READ_DEVMASK`, and obtains volume levels via `SOUND_MIXER_READ_VOLUME`.

Device names are constructed from `ci.longname` and `ci.hw_info` fields, while the platform API string derives from `/dev/sndstat`. The implementation respects the `hw.snd.default_unit` sysctl to identify the primary sound card, flagging it as `main` in the output structure.

### Haiku Media Kit

For Haiku OS, [`src/detection/sound/sound_haiku.cpp`](https://github.com/fastfetch-cli/fastfetch/blob/main/src/detection/sound/sound_haiku.cpp) uses the **Media Kit** (`BMediaRoster`) to access the audio output node. It extracts the node name and identifier, then navigates the `BParameterWeb` to locate the master gain parameter, converting the linear gain value to a percentage for the volume field.

### Fallback for Unsupported Platforms

When compiled for platforms without specific audio detection support, [`src/detection/sound/sound_nosupport.c`](https://github.com/fastfetch-cli/fastfetch/blob/main/src/detection/sound/sound_nosupport.c) provides a stub implementation returning `"Fastfetch was built without sound detection support"`, ensuring graceful degradation rather than build failures.

## The FFSoundDevice Data Structure

All platform implementations populate the same **uniform data structure** defined in [`src/detection/sound/sound.h`](https://github.com/fastfetch-cli/fastfetch/blob/main/src/detection/sound/sound.h):

```c
typedef struct FFSoundDevice {
    FFstrbuf identifier;   // Unique ID (PulseAudio sink name, CoreAudio UID, etc.)
    FFstrbuf name;         // Human-readable device name
    FFstrbuf platformApi;  // "PulseAudio", "Core Audio", "OSS", "MMDevice"
    uint8_t  volume;       // 0-100 or FF_SOUND_VOLUME_UNKNOWN
    bool     active;       // Device is currently active/streaming
    bool     main;         // System default output device
} FFSoundDevice;

```

This abstraction allows the presentation layer in [`src/modules/sound/sound.c`](https://github.com/fastfetch-cli/fastfetch/blob/main/src/modules/sound/sound.c) to filter devices based on user preferences (main only, active only, or all devices) without platform-specific logic.

## Using the Sound Detection API Programmatically

You can leverage Fastfetch's detection engine in custom C applications by including the detection headers and linking against the appropriate libraries:

```c
#include "fastfetch.h"
#include "detection/sound/sound.h"

int main(void) {
    FFlist devices = ffListCreate(sizeof(FFSoundDevice));
    
    const char *err = ffDetectSound(&devices);
    if (err) {
        fprintf(stderr, "Detection failed: %s\n", err);
        return 1;
    }
    
    FF_LIST_FOR_EACH(FFSoundDevice, dev, devices) {
        printf("%s – %s – %u%% – %s\n",
               dev->identifier.chars,
               dev->name.chars,
               dev->volume,
               dev->platformApi.chars);
    }
    
    // Cleanup required for FFstrbuf members
    FF_LIST_FOR_EACH(FFSoundDevice, dev, devices) {
        ffStrbufDestroy(&dev->identifier);
        ffStrbufDestroy(&dev->name);
        ffStrbufDestroy(&dev->platformApi);
    }
    ffListDestroy(&devices);
    return 0;
}

```

Compile with the same feature flags used by Fastfetch (e.g., `-DFF_HAVE_PULSE=1`) to enable the corresponding backend.

## Summary

- **Modular architecture**: Fastfetch uses `ffDetectSound()` in [`src/detection/sound/sound.h`](https://github.com/fastfetch-cli/fastfetch/blob/main/src/detection/sound/sound.h) to abstract platform differences behind a unified API.
- **Dynamic loading**: Linux avoids hard dependencies by dynamically loading libpulse at runtime rather than linking at build time.
- **Native APIs**: Each platform uses the "right" API—Core Audio for Apple systems, MMDevice for Windows, OSS for BSD, and PulseAudio for Linux.
- **Uniform data model**: All implementations populate `FFSoundDevice` structures with identifier, name, volume, active state, and main/default flags.
- **Compile-time selection**: Feature macros like `FF_HAVE_PULSE` and `FF_HAVE_COREAUDIO` determine which backends are built into the binary.

## Frequently Asked Questions

### How does Fastfetch choose which audio API to use?

Fastfetch selects the audio API at **compile time** using preprocessor macros. The build system detects available system headers and defines flags like `FF_HAVE_PULSE` for Linux or `FF_HAVE_COREAUDIO` for macOS. The generic detection header then includes the appropriate implementation file from `src/detection/sound/`, ensuring only relevant code compiles into the final binary.

### Can Fastfetch detect sound cards without PulseAudio on Linux?

No. As implemented in [`src/detection/sound/sound_linux.c`](https://github.com/fastfetch-cli/fastfetch/blob/main/src/detection/sound/sound_linux.c), Fastfetch currently requires **PulseAudio** (or PipeWire's PulseAudio compatibility layer) for Linux sound detection. If compiled without `FF_HAVE_PULSE`, the module returns a "built without libpulse support" message. There is no ALSA-only backend in the current source tree.

### What information does Fastfetch retrieve about sound cards?

Fastfetch extracts the **device identifier** (unique hardware ID), **human-readable name**, **current volume percentage**, **active state** (whether audio is currently playing through the device), and **main/default status** (indicating the system default output). It also records the **platform API** used for detection (e.g., "PulseAudio" or "Core Audio") to aid in debugging.

### Is the sound detection logic available as a standalone library?

While Fastfetch's detection code is **modular and reusable**, it is not distributed as a separate library. The detection functions in `src/detection/sound/` depend on Fastfetch's internal utilities (like `FFstrbuf` and `FFlist`). However, you can extract the relevant files ([`sound.h`](https://github.com/fastfetch-cli/fastfetch/blob/main/sound.h), platform-specific `.c` files, and [`fflibrary.c`](https://github.com/fastfetch-cli/fastfetch/blob/main/fflibrary.c) for dynamic loading) into your own project under the MIT license, maintaining the architectural dependencies.