跨平臺實時音頻驅動：libsoundio

libsoundio 是輕量級抽象的聲音驅動程序，是一個跨平臺實時音頻輸入和輸出的 C99 庫。libsoundio 提供文檔完善的 API，適用于實時軟件，比如游戲，數字音頻工作站，音樂播放器等等實用工具。

libsoundio 非常健壯，可以正確處理內存不足的狀態。

特性&限制

• 支持的后端

• JACK

• PulseAudio

• ALSA

• CoreAudio

• WASAPI

• Dummy (silence)

• 支持原始設備和共享設備

• 支持設備 ID 和友好的名字

• 支持優化每個后端的使用

• C 語言庫，僅僅依賴于后端 API 庫和 libc

  
  

• 支持頻道布局

基礎正弦波示例

#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 += seconds_per_frame * frame_count;
        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;
}

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