使用ALSA驱动进行录音和播放(Ubuntu22)

本文介绍了ALSA的最简单的使用案例，包含录音和播放。

安装ALSA开发库

sudo apt update
sudo apt install libasound2-dev

最简示例代码

1. 录音示例代码(record.c)

#include <alsa/asoundlib.h>
#include <signal.h>

unsigned int SAMPLE_RATE = 44100;
#define CHANNELS 2
#define FORMAT SND_PCM_FORMAT_S16_LE
#define BUFFER_FRAMES 1024

volatile sig_atomic_t stop_recording = 0;

void handle_signal(int sig) {
    stop_recording = 1;
}

int main() {
    snd_pcm_t *handle;
    snd_pcm_hw_params_t *params;
    FILE *file = fopen("audio.raw", "wb");

    // 打开默认录音设备
    if (snd_pcm_open(&handle, "default", SND_PCM_STREAM_CAPTURE, 0) < 0) {
        fprintf(stderr, "无法打开PCM设备\n");
        return 1;
    }

    // 分配硬件参数结构体
    snd_pcm_hw_params_alloca(&params);
    snd_pcm_hw_params_any(handle, params);

    // 设置参数
    snd_pcm_hw_params_set_access(handle, params, SND_PCM_ACCESS_RW_INTERLEAVED);
    snd_pcm_hw_params_set_format(handle, params, FORMAT);
    snd_pcm_hw_params_set_channels(handle, params, CHANNELS);
    snd_pcm_hw_params_set_rate_near(handle, params, &SAMPLE_RATE, 0);

    // 应用参数
    if (snd_pcm_hw_params(handle, params) < 0) {
        fprintf(stderr, "无法设置参数\n");
        return 1;
    }

    char buffer[BUFFER_FRAMES * CHANNELS * 2]; // 16位 = 2字节
    printf("开始录音... 按Enter停止\n");

    while (!stop_recording) {
        int frames = snd_pcm_readi(handle, buffer, BUFFER_FRAMES);
        if (frames < 0) frames = snd_pcm_recover(handle, frames, 0);
        if (frames < 0) break;
        
        fwrite(buffer, sizeof(char), frames * CHANNELS * 2, file);
    }

    // 清理
    snd_pcm_drop(handle);
    snd_pcm_close(handle);
    fclose(file);
    printf("录音完成！保存为audio.raw\n");
    return 0;
}

2.播放示例代码(play.c)

#include <alsa/asoundlib.h>

unsigned int SAMPLE_RATE = 44100;
#define CHANNELS 2
#define FORMAT SND_PCM_FORMAT_S16_LE
#define BUFFER_FRAMES 1024

int main() {
    snd_pcm_t *handle;
    snd_pcm_hw_params_t *params;
    FILE *file = fopen("audio.raw", "rb");

    // 打开默认播放设备
    if (snd_pcm_open(&handle, "default", SND_PCM_STREAM_PLAYBACK, 0) < 0) {
        fprintf(stderr, "无法打开PCM设备\n");
        return 1;
    }

    // 设置参数（与录音参数一致）
    snd_pcm_hw_params_alloca(&params);
    snd_pcm_hw_params_any(handle, params);
    
    snd_pcm_hw_params_set_access(handle, params, SND_PCM_ACCESS_RW_INTERLEAVED);
    snd_pcm_hw_params_set_format(handle, params, FORMAT);
    snd_pcm_hw_params_set_channels(handle, params, CHANNELS);
    snd_pcm_hw_params_set_rate_near(handle, params, &SAMPLE_RATE, 0);

    if (snd_pcm_hw_params(handle, params) < 0) {
        fprintf(stderr, "无法设置参数\n");
        return 1;
    }

    char buffer[BUFFER_FRAMES * CHANNELS * 2];
    printf("开始播放...\n");

    while (!feof(file)) {
        size_t read = fread(buffer, sizeof(char), sizeof(buffer), file);
        if (read == 0) break;
        
        int frames = read / (CHANNELS * 2);
        int written = snd_pcm_writei(handle, buffer, frames);
        if (written < 0) written = snd_pcm_recover(handle, written, 0);
        if (written < 0) break;
    }

    // 清理
    snd_pcm_drain(handle);
    snd_pcm_close(handle);
    fclose(file);
    printf("播放完成！\n");
    return 0;
}

编译和运行

编译：

gcc record.c -o record -lasound
gcc play.c -o play -lasound

运行：

1. 录音：./record（按Ctrl+C停止）
2. 播放：./play

参数说明：

• SAMPLE_RATE: 44100Hz (CD音质)
• CHANNELS: 2 (立体声)
• FORMAT: 16位小端格式
• BUFFER_FRAMES: ALSA缓冲区大小

文件格式：

• 使用原始PCM格式（无文件头）
• 可用Audacity导入：文件 > 导入 > 原始数据，参数设置与代码中一致