Linux下对于不同WAV文件的播放,有的放出来全是噪音

Neko_zxh 发布于 2017/06/23 16:52
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使用网上博客的一个最简单的关于wav文件的播放程序,然而播放对于有的wav文件可以播放,有的播放全是杂音,采样率更改为44.1khz,还有哪里是需要注意的?

/**
*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_U8);
	if (ret < 0) {
		perror("snd_pcm_hw_params_set_format");
		exit(1);
	}
	//6. 设置采样率

	val = 44100;
	//val = 8000;
	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
	ret = snd_pcm_hw_params_set_channels(playback_handle, hw_params, 2);
	if (ret < 0) {
		perror("snd_pcm_hw_params_set_channels");
		exit(1);
	}
	
	/* Set period size to 32 frames. */
    frames = 32;
    periodsize = frames * 2;
    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。

 

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