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MIT License GNU LESSER GENERAL PUBLIC LICENSE
Version 2.1, February 1999
Copyright (c) 2025 Emil Lerch Copyright (C) 1991, 1999 Free Software Foundation, Inc.
51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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That's all there is to it!

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# Static ALSA Library for Zig
A minimal, self-contained static build of ALSA (Advanced Linux Sound Architecture) designed for embedding in Zig applications.
## What This Library Provides
### Included Components
- **Core ALSA**: Configuration, error handling, async operations
- **PCM (Audio Playback/Recording)**: Hardware access, format conversion, routing
- **Control**: Hardware mixer controls, card enumeration
- **Timer**: Hardware timer access
- **Built-in Plugins**: Essential audio processing without dynamic loading
### Built-in PCM Plugins
- `hw` - Direct hardware access
- `copy` - Simple audio copying
- `linear` - Linear format conversion
- `null` - Null audio sink
- `empty` - Empty audio source
- `adpcm` - ADPCM compression
- `alaw` - A-law compression
- `mulaw` - μ-law compression
- `iec958` - S/PDIF digital audio
- `lfloat` - Linear floating point conversion
- `mmap_emul` - Memory mapping emulation
- `route` - Audio channel routing
## Limitations
### What's NOT Included
- **Dynamic Plugin Loading**: No `dlopen()` support - only built-in plugins work
- **Complex Plugins**: No `dmix`, `dsnoop`, `pulse`, `jack` plugins
- **Rate Conversion**: No `rate` plugin (would need external rate converter)
- **Advanced Routing**: No `multi`, `asym` plugins
- **Software Volume**: No `softvol` plugin
- **File I/O**: No `file` plugin for audio recording to disk
### Audio Limitations
- Only direct hardware access (`hw:X,Y`) and built-in conversions
- No automatic sample rate conversion
- No software mixing of multiple streams
- No PulseAudio/JACK integration
## Integration into Zig Projects
### 1. Add as Dependency
In your `build.zig.zon`:
```zig
.dependencies = .{
.alsa = .{
.path = "../path/to/0-alsa-lib",
},
},
```
### 2. Link in build.zig
```zig
const std = @import("std");
pub fn build(b: *std.Build) void {
const exe = b.addExecutable(.{
.name = "my-audio-app",
.root_source_file = b.path("src/main.zig"),
.target = target,
.optimize = optimize,
});
// Add ALSA dependency
const alsa_dep = b.dependency("alsa", .{});
const alsa_lib = alsa_dep.artifact("asound");
exe.linkLibC();
exe.linkLibrary(alsa_lib);
exe.addIncludePath(alsa_dep.path("zig-out/include"));
b.installArtifact(exe);
}
```
### 3. Basic Usage Example
```zig
const std = @import("std");
const c = @cImport({
@cInclude("alsa/asoundlib.h");
});
pub fn main() !void {
var pcm: ?*c.snd_pcm_t = null;
// Open PCM device for recording
const result = c.snd_pcm_open(
&pcm,
"hw:0,0", // Card 0, Device 0
c.SND_PCM_STREAM_CAPTURE,
0
);
if (result < 0) {
std.log.err("Cannot open audio device: {s}", .{c.snd_strerror(result)});
return;
}
defer _ = c.snd_pcm_close(pcm);
// Configure PCM parameters
var params: ?*c.snd_pcm_hw_params_t = null;
_ = c.snd_pcm_hw_params_malloc(&params);
defer c.snd_pcm_hw_params_free(params);
_ = c.snd_pcm_hw_params_any(pcm, params);
_ = c.snd_pcm_hw_params_set_access(pcm, params, c.SND_PCM_ACCESS_RW_INTERLEAVED);
_ = c.snd_pcm_hw_params_set_format(pcm, params, c.SND_PCM_FORMAT_S16_LE);
_ = c.snd_pcm_hw_params_set_channels(pcm, params, 1);
var rate: c_uint = 16000;
_ = c.snd_pcm_hw_params_set_rate_near(pcm, params, &rate, null);
_ = c.snd_pcm_hw_params(pcm, params);
// Read audio data
var buffer: [1024]i16 = undefined;
const frames_read = c.snd_pcm_readi(pcm, &buffer, buffer.len / 2);
std.log.info("Read {} frames", .{frames_read});
}
```
## Configuration
### ALSA Configuration File
The library uses ALSA's configuration system. The configuration file defines how device names are resolved and what plugins are available.
**Critical**: Without proper configuration, even basic `hw:X,Y` device access may fail.
```bash
# Set custom config path (recommended)
export ALSA_CONFIG_PATH=/path/to/your/alsa.conf
# Run your application
./my-audio-app
# Or disable config entirely (hardware-only, may not work)
export ALSA_CONFIG_PATH=/dev/null
```
### Example alsa.conf (Minimal Working Configuration)
This is the minimal configuration needed for `hw:X,Y` device access:
```
# Essential: Define the hw PCM type
pcm.hw {
@args [ CARD DEV SUBDEV ]
@args.CARD {
type string
default 0
}
@args.DEV {
type integer
default 0
}
@args.SUBDEV {
type integer
default -1
}
type hw
card $CARD
device $DEV
subdevice $SUBDEV
}
# Optional: Define default devices
pcm.!default {
type hw
card 0
device 0
}
ctl.!default {
type hw
card 0
}
# Optional: Define named devices
pcm.microphone {
type hw
card 3
device 0
}
```
### Configuration Behavior
- **With minimal alsa.conf**: `hw:X,Y` device access works
- **Without alsa.conf** (`ALSA_CONFIG_PATH=/dev/null`): May fail with "Unknown PCM" errors
- **With system config**: May fail if it references plugins not built into this static library
## Device Selection
### Hardware Device Format
```
hw:CARD,DEVICE
```
Examples:
- `hw:0,0` - Card 0, Device 0 (usually built-in audio)
- `hw:1,0` - Card 1, Device 0 (usually USB audio)
- `hw:3,0` - Card 3, Device 0 (specific USB device)
### Finding Available Devices
```bash
# List audio cards
cat /proc/asound/cards
# List PCM devices
cat /proc/asound/pcm
# Test device access
aplay -l # playback devices
arecord -l # capture devices
```
## Build Configuration
The library is configured for static linking with these key settings:
```zig
// In build.zig - these are already set
.HAVE_LIBDL = 1, // Keep dlmisc.c but use static symbols
.BUILD_PCM_PLUGIN_* = "1", // Enable built-in plugins
// PIC undefined // Enable static plugin symbols
```
### Compiler Flags
- `-DALSA_STATIC` - Static library build
- `-DBUILD_STATIC_ONLY` - No shared library support
- `-UPIC` - Undefine PIC to enable built-in plugin symbols
## Troubleshooting
### Common Issues
1. **"Unknown PCM device"**
- Device doesn't exist or wrong card/device number
- Check `/proc/asound/cards` and `/proc/asound/pcm`
2. **"No such device or address"**
- Device is busy or doesn't support the requested format
- Try different sample rate/format or check if device is in use
3. **"Cannot open shared library [builtin]"**
- PIC is defined - this shouldn't happen with this build
- Indicates dynamic loading attempt (build configuration error)
### Debug Environment Variables
```bash
# Enable ALSA debug output
export ALSA_DEBUG=1
# Use minimal config
export ALSA_CONFIG_PATH=/dev/null
# Specify custom config
export ALSA_CONFIG_PATH=./my-alsa.conf
```
## Performance Characteristics
- **Memory**: ~200KB static library
- **Latency**: Direct hardware access (no software mixing overhead)
- **CPU**: Minimal - only format conversion overhead for built-in plugins
- **Compatibility**: Works with any ALSA-compatible hardware
## License
This static build follows the original ALSA library licensing (LGPL 2.1+).

46
build.zig
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@ -19,20 +19,33 @@ pub fn build(b: *std.Build) void {
.HAVE_SYS_SHM_H = 1, .HAVE_SYS_SHM_H = 1,
.HAVE_MALLOC_H = 1, .HAVE_MALLOC_H = 1,
.HAVE_LFS = 1, .HAVE_LFS = 1,
.HAVE_LIBDL = 1, .HAVE_LIBDL = 1, // Match native build
.PIC = 1, // .PIC = 0, // Remove PIC entirely to enable builtin symbols
.BUILD_PCM = "1", .BUILD_PCM = "1",
.BUILD_MIXER = "1", .BUILD_MIXER = "1",
.BUILD_HWDEP = "1", .BUILD_HWDEP = "1",
.ENABLE_STATIC = 1, // Match --enable-static=yes
.ENABLE_SHARED = 0, // Match --enable-shared=no
.ALSA_DEVICE_DIRECTORY = "/dev/snd/", .ALSA_DEVICE_DIRECTORY = "/dev/snd/",
.ALSA_CONFIG_DIR = "/usr/share/alsa", .ALSA_CONFIG_DIR = "/usr/share/alsa",
.ALSA_PLUGIN_DIR = "/usr/lib/alsa-lib", .ALSA_PLUGIN_DIR = "/usr/lib/alsa-lib",
.SND_MAX_CARDS = 32, .SND_MAX_CARDS = 32,
.BUILD_PCM_PLUGIN_ADPCM = "1",
.BUILD_PCM_PLUGIN_ALAW = "1",
.BUILD_PCM_PLUGIN_IEC958 = "1",
.BUILD_PCM_PLUGIN_LFLOAT = "1",
.BUILD_PCM_PLUGIN_MMAP_EMUL = "1",
.BUILD_PCM_PLUGIN_MULAW = "1",
.BUILD_PCM_PLUGIN_RATE = "1",
.BUILD_PCM_PLUGIN_ROUTE = "1",
.__SYMBOL_PREFIX = "", .__SYMBOL_PREFIX = "",
._GNU_SOURCE = 1, ._GNU_SOURCE = 1,
.HAVE_GNU_LD = 1, .HAVE_GNU_LD = 1,
.HAVE_ELF = 1, .HAVE_ELF = 1,
.HAVE_ASM_PREVIOUS_DIRECTIVE = 1, .HAVE_ASM_PREVIOUS_DIRECTIVE = 1,
.BUILD_STATIC = 1,
.BUILD_PCM_PLUGIN_HW = 1,
.SND_PCM_BUILTIN = 1,
}); });
// Create version.h // Create version.h
@ -102,6 +115,8 @@ pub fn build(b: *std.Build) void {
lib.addConfigHeader(config); lib.addConfigHeader(config);
lib.addIncludePath(upstream.path("include")); lib.addIncludePath(upstream.path("include"));
lib.addIncludePath(upstream.path("src/pcm")); // For pcm_rate.h etc
lib.addIncludePath(b.path(".")); // For our pcm_symbols_list.c
lib.addIncludePath(version_h.getDirectory()); lib.addIncludePath(version_h.getDirectory());
lib.addIncludePath(asoundlib_h.getDirectory()); lib.addIncludePath(asoundlib_h.getDirectory());
@ -136,17 +151,44 @@ pub fn build(b: *std.Build) void {
"src/control/setup.c", "src/control/setup.c",
"src/control/ctlparse.c", "src/control/ctlparse.c",
"src/control/eld.c", "src/control/eld.c",
"src/control/control_empty.c", // Empty control
"src/pcm/pcm.c", "src/pcm/pcm.c",
"src/pcm/pcm_hw.c", "src/pcm/pcm_hw.c",
"src/pcm/pcm_params.c", "src/pcm/pcm_params.c",
"src/pcm/pcm_misc.c", "src/pcm/pcm_misc.c",
"src/pcm/pcm_mmap.c", "src/pcm/pcm_mmap.c",
"src/pcm/pcm_generic.c",
"src/pcm/pcm_simple.c",
"src/pcm/pcm_plug.c",
"src/pcm/mask.c", "src/pcm/mask.c",
"src/pcm/interval.c", "src/pcm/interval.c",
// Core PCM plugins - must match native build
"src/pcm/pcm_copy.c",
"src/pcm/pcm_linear.c",
"src/pcm/pcm_null.c",
"src/pcm/pcm_empty.c",
"src/pcm/pcm_adpcm.c",
"src/pcm/pcm_alaw.c",
"src/pcm/pcm_mulaw.c",
"src/pcm/pcm_iec958.c",
"src/pcm/pcm_lfloat.c",
"src/pcm/pcm_mmap_emul.c",
"src/pcm/pcm_route.c",
"src/pcm/pcm_plugin.c", // Plugin support functions
"src/pcm/pcm_symbols.c", // Builtin plugin registration
"src/control/control_symbols.c", // Control symbols
"src/timer/timer_symbols.c", // Timer symbols
"src/timer/timer.c",
"src/timer/timer_hw.c",
"src/timer/timer_query.c",
"src/timer/timer_query_hw.c",
}, },
.flags = &.{ .flags = &.{
"-D_GNU_SOURCE", "-D_GNU_SOURCE",
"-DALSA_LIBRARY_BUILD", "-DALSA_LIBRARY_BUILD",
"-DALSA_STATIC",
"-DBUILD_STATIC_ONLY",
"-UPIC", // Explicitly undefine PIC to enable builtin symbols
}, },
}); });

1
ctl_symbols_list.c Normal file
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@ -0,0 +1 @@
// Empty - control_empty is already included in the main list

11
pcm_symbols_list.c Normal file
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@ -0,0 +1,11 @@
&_snd_module_pcm_copy,
&_snd_module_pcm_linear,
&_snd_module_pcm_null,
&_snd_module_pcm_empty,
&_snd_module_pcm_adpcm,
&_snd_module_pcm_alaw,
&_snd_module_pcm_mulaw,
&_snd_module_pcm_iec958,
&_snd_module_pcm_lfloat,
&_snd_module_pcm_mmap_emul,
&_snd_module_pcm_route,

1
timer_symbols_list.c Normal file
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@ -0,0 +1 @@
&_snd_module_timer_hw,