/**

*test.c

*

*注意：这个例子在Ubuntu 12.04.1环境下编译运行成功。

*

*/

#include <stdio.h>

#include <stdlib.h>

#include <alsa/asoundlib.h>

int main(int argc, char *argv[])

{

    int i;

    int ret;

    int buf[128];

    unsigned int val;

    int dir=0;

    char *buffer;

    int size;

    snd_pcm_uframes_t frames;

    snd_pcm_uframes_t periodsize;

    snd_pcm_t *playback_handle;//PCM设备句柄pcm.h

    snd_pcm_hw_params_t *hw_params;//硬件信息和PCM流配置

    if (argc != 2) {

        printf("error: alsa_play_test [music name]\n");

        exit(1);

    }

    printf("play song %s by wolf\n", argv[1]);

    FILE *fp = fopen(argv[1], "rb");

    if(fp == NULL)

    return 0;

    fseek(fp, 100, SEEK_SET);

    //1. 打开PCM，最后一个参数为0意味着标准配置

    ret = snd_pcm_open(&playback_handle, "default", SND_PCM_STREAM_PLAYBACK, 0);

    if (ret < 0) {

        perror("snd_pcm_open");

        exit(1);

    }

    //2. 分配snd_pcm_hw_params_t结构体

    ret = snd_pcm_hw_params_malloc(&hw_params);

    if (ret < 0) {

        perror("snd_pcm_hw_params_malloc");

        exit(1);

    }

    //3. 初始化hw_params

    ret = snd_pcm_hw_params_any(playback_handle, hw_params);

    if (ret < 0) {

        perror("snd_pcm_hw_params_any");

        exit(1);

    }

    //4. 初始化访问权限

    ret = snd_pcm_hw_params_set_access(playback_handle, hw_params, SND_PCM_ACCESS_RW_INTERLEAVED);

    if (ret < 0) {

        perror("snd_pcm_hw_params_set_access");

        exit(1);

    }

    //5. 初始化采样格式SND_PCM_FORMAT_U8,8位

    ret = snd_pcm_hw_params_set_format(playback_handle, hw_params, SND_PCM_FORMAT_S16_LE);

    if (ret < 0) {

        perror("snd_pcm_hw_params_set_format");

        exit(1);

    }

    //6. 设置采样率，如果硬件不支持我们设置的采样率，将使用最接近的

    //val = 44100,有些录音采样频率固定为8KHz

    val = 16000;

    ret = snd_pcm_hw_params_set_rate_near(playback_handle, hw_params, &val, &dir);

    if (ret < 0) {

        perror("snd_pcm_hw_params_set_rate_near");

        exit(1);

    }

    //7. 设置通道数量  1

    ret = snd_pcm_hw_params_set_channels(playback_handle, hw_params, 1);

    if (ret < 0) {

        perror("snd_pcm_hw_params_set_channels");

        exit(1);

    }

    /* Set period size to 32 frames. */

    frames = 32;

    periodsize = frames ;

    ret = snd_pcm_hw_params_set_buffer_size_near(playback_handle, hw_params, &periodsize);

    if (ret < 0)

    {

         printf("Unable to set buffer size %li : %s\n", frames * 2, snd_strerror(ret));

    }

    periodsize /= 2;

    ret = snd_pcm_hw_params_set_period_size_near(playback_handle, hw_params, &periodsize, 0);

    if (ret < 0)

    {

        printf("Unable to set period size %li : %s\n", periodsize,  snd_strerror(ret));

    }

    //8. 设置hw_params

    ret = snd_pcm_hw_params(playback_handle, hw_params);

    if (ret < 0) {

        perror("snd_pcm_hw_params");

        exit(1);

    }

     /* Use a buffer large enough to hold one period */

    snd_pcm_hw_params_get_period_size(hw_params, &frames, &dir);

    size = frames * 2; /* 2 bytes/sample, 2 channels */

    buffer = (char *) malloc(size);

    fprintf(stderr,

            "size = %d\n",

            size);

    while (1)

    {

        ret = fread(buffer, 1, size, fp);

        if(ret == 0)

        {

              fprintf(stderr, "end of file on input\n");

              break;

        }

        else if (ret != size)

        {

        }

        //9. 写音频数据到PCM设备

        while(ret = snd_pcm_writei(playback_handle, buffer, frames)<0)

        {

            usleep(2000);

            if (ret == -EPIPE)

            {

                  /* EPIPE means underrun */

                  fprintf(stderr, "underrun occurred\n");

                  //完成硬件参数设置，使设备准备好

                  snd_pcm_prepare(playback_handle);

            }

            else if (ret < 0)

            {

                  fprintf(stderr,

                      "error from writei: %s\n",

                      snd_strerror(ret));

            }

        }

    }

    //10. 关闭PCM设备句柄

    snd_pcm_close(playback_handle);

    return 0;

}

//注意：编译的时候应该保持“gcc -o test test.c -L. -lasound”的格式，运行的时候应该保持"./test clip2.wav"这种格式。