Home

Awesome

libsoundio

C library providing cross-platform audio input and output. The API is suitable for real-time software such as digital audio workstations as well as consumer software such as music players.

This library is an abstraction; however in the delicate balance between performance and power, and API convenience, the scale is tipped closer to the former. Features that only exist in some sound backends are exposed.

Features and Limitations

Synopsis

Complete program to emit a sine wave over the default device using the best backend:

#include <soundio/soundio.h>

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>

static const float PI = 3.1415926535f;
static float seconds_offset = 0.0f;
static void write_callback(struct SoundIoOutStream *outstream,
        int frame_count_min, int frame_count_max)
{
    const struct SoundIoChannelLayout *layout = &outstream->layout;
    float float_sample_rate = outstream->sample_rate;
    float seconds_per_frame = 1.0f / float_sample_rate;
    struct SoundIoChannelArea *areas;
    int frames_left = frame_count_max;
    int err;

    while (frames_left > 0) {
        int frame_count = frames_left;

        if ((err = soundio_outstream_begin_write(outstream, &areas, &frame_count))) {
            fprintf(stderr, "%s\n", soundio_strerror(err));
            exit(1);
        }

        if (!frame_count)
            break;

        float pitch = 440.0f;
        float radians_per_second = pitch * 2.0f * PI;
        for (int frame = 0; frame < frame_count; frame += 1) {
            float sample = sinf((seconds_offset + frame * seconds_per_frame) * radians_per_second);
            for (int channel = 0; channel < layout->channel_count; channel += 1) {
                float *ptr = (float*)(areas[channel].ptr + areas[channel].step * frame);
                *ptr = sample;
            }
        }
        seconds_offset = fmodf(seconds_offset +
            seconds_per_frame * frame_count, 1.0f);

        if ((err = soundio_outstream_end_write(outstream))) {
            fprintf(stderr, "%s\n", soundio_strerror(err));
            exit(1);
        }

        frames_left -= frame_count;
    }
}

int main(int argc, char **argv) {
    int err;
    struct SoundIo *soundio = soundio_create();
    if (!soundio) {
        fprintf(stderr, "out of memory\n");
        return 1;
    }

    if ((err = soundio_connect(soundio))) {
        fprintf(stderr, "error connecting: %s", soundio_strerror(err));
        return 1;
    }

    soundio_flush_events(soundio);

    int default_out_device_index = soundio_default_output_device_index(soundio);
    if (default_out_device_index < 0) {
        fprintf(stderr, "no output device found");
        return 1;
    }

    struct SoundIoDevice *device = soundio_get_output_device(soundio, default_out_device_index);
    if (!device) {
        fprintf(stderr, "out of memory");
        return 1;
    }

    fprintf(stderr, "Output device: %s\n", device->name);

    struct SoundIoOutStream *outstream = soundio_outstream_create(device);
    outstream->format = SoundIoFormatFloat32NE;
    outstream->write_callback = write_callback;

    if ((err = soundio_outstream_open(outstream))) {
        fprintf(stderr, "unable to open device: %s", soundio_strerror(err));
        return 1;
    }

    if (outstream->layout_error)
        fprintf(stderr, "unable to set channel layout: %s\n", soundio_strerror(outstream->layout_error));

    if ((err = soundio_outstream_start(outstream))) {
        fprintf(stderr, "unable to start device: %s", soundio_strerror(err));
        return 1;
    }

    for (;;)
        soundio_wait_events(soundio);

    soundio_outstream_destroy(outstream);
    soundio_device_unref(device);
    soundio_destroy(soundio);
    return 0;
}

Backend Priority

When you use soundio_connect, libsoundio tries these backends in order. If unable to connect to that backend, due to the backend not being installed, or the server not running, or the platform is wrong, the next backend is tried.

  1. JACK
  2. PulseAudio
  3. ALSA (Linux)
  4. CoreAudio (OSX)
  5. WASAPI (Windows)
  6. Dummy

If you don't like this order, you can use soundio_connect_backend to explicitly choose a backend to connect to. You can use soundio_backend_count and soundio_get_backend to get the list of available backends.

API Documentation

Building

Install the dependencies:

mkdir build
cd build
cmake ..
make
sudo make install

Building for Windows

You can build libsoundio with mxe. Follow the requirements section to install the packages necessary on your system. Then somewhere on your file system:

git clone https://github.com/mxe/mxe
cd mxe
make MXE_TARGETS='x86_64-w64-mingw32.static i686-w64-mingw32.static' gcc

Then in the libsoundio source directory (replace "/path/to/mxe" with the appropriate path):

mkdir build-win32
cd build-win32
cmake .. -DCMAKE_TOOLCHAIN_FILE=/path/to/mxe/usr/i686-w64-mingw32.static/share/cmake/mxe-conf.cmake
make

mkdir build-win64
cd build-win64
cmake .. -DCMAKE_TOOLCHAIN_FILE=/path/to/mxe/usr/x86_64-w64-mingw32.static/share/cmake/mxe-conf.cmake
make

Testing

For each backend, do the following:

  1. Run the unit tests: ./unit_tests. To see test coverage, install lcov, run make coverage, and then view coverage/index.html in a browser.
  2. Run the example ./sio_list_devices and make sure it does not crash, and the output looks good. If valgrind is available, use it.
  3. Run ./sio_list_devices --watch and make sure it detects when you plug and unplug a USB microphone.
  4. Run ./sio_sine and make sure you hear a sine wave. For backends with raw devices, run ./sio_sine --device id --raw (where 'id' is a device id you got from sio_list_devices and make sure you hear a sine wave.
    • Use 'p' to test pausing, 'u' to test unpausing, 'q' to test cleanup.
    • 'c' for clear buffer. Clear buffer should not pause the stream and it should also not cause an underflow.
    • Use 'P' to test pausing from the callback, and then 'u' to unpause.
  5. Run ./underflow and read the testing instructions that it prints.
  6. Run ./sio_microphone and ensure that it is both recording and playing back correctly. If possible use the --in-device and --out-device parameters to test a USB microphone in raw mode.
  7. Run ./backend_disconnect_recover and read the testing instructions that it prints.
  8. Run ./latency and make sure the printed beeps line up with the beeps that you hear.

Building the Documentation

Ensure that doxygen is installed, then:

make doc

Then look at html/index.html in a browser.