基于Linux ALSA音频驱动的wav文件解析及播放程序 2012
本设计思路：先打开一个普通wav音频文件，从定义的文件头前面的44个字节中，取出文件头的定义消息，置于一个文件头的结构体中。然后打开alsa音频驱动，从文件头结构体取出采样精度，声道数，采样频率三个重要参数，利用alsa音频驱动的API设置好参数，最后打开wav文件，定位到数据区，把音频数据依次写到音频驱动中去，开始播放，当写入完成后，退出写入的循环。
注意：本设计需要alsa的libasound-dev的库，编译链接时需要连接 —lasound.
#include<stdio.h>
#include<stdlib.h>
#include <string.h>
#include <alsa/asoundlib.h>
struct WAV_HEADER
{
char rld[4]; //riff 标志符号
int rLen;
char wld[4]; //格式类型（wave）
char fld[4]; //"fmt"
int fLen; //sizeof(wave format matex)
short wFormatTag; //编码格式
short wChannels; //声道数
int nSamplesPersec ; //采样频率
int nAvgBitsPerSample;//WAVE文件采样大小
short wBlockAlign; //块对齐
short wBitsPerSample; //WAVE文件采样大小
char dld[4]; //”data“
int wSampleLength; //音频数据的大小
} wav_header;
int set_pcm_play(FILE *fp);
int main(int argc,char *argv[])
{
if(argc!=2)
{
printf("Usage:wav-player+wav file name\n");
exit(1);
}
int nread;
FILE *fp;
fp=fopen(argv[1],"rb");
if(fp==NULL)
{
perror("open file failed:\n");
exit(1);
}
nread=fread(&wav_header,1,sizeof(wav_header),fp);
printf("nread=%d\n",nread);
//printf("RIFF 标志%s\n",wav_header.rld);
printf("文件大小rLen：%d\n",wav_header.rLen);
//printf("wld=%s\n",wav_header.wld);
//printf("fld=%s\n",wav_header.fld);
// printf("fLen=%d\n",wav_header.fLen);
//printf("wFormatTag=%d\n",wav_header.wFormatTag);
printf("声道数：%d\n",wav_header.wChannels);
printf("采样频率：%d\n",wav_header.nSamplesPersec);
//printf("nAvgBitsPerSample=%d\n",wav_header.nAvgBitsPerSample);
//printf("wBlockAlign=%d\n",wav_header.wBlockAlign);
printf("采样的位数：%d\n",wav_header.wBitsPerSample);
// printf("data=%s\n",wav_header.dld);
printf("wSampleLength=%d\n",wav_header.wSampleLength);
set_pcm_play(fp);
return 0;
}
int set_pcm_play(FILE *fp)
{
int rc;
int ret;
int size;
snd_pcm_t* handle; //PCI设备句柄
snd_pcm_hw_params_t* params;//硬件信息和PCM流配置
unsigned int val;
int dir=0;
snd_pcm_uframes_t frames;
char *buffer;
int channels=wav_header.wChannels;
int frequency=wav_header.nSamplesPersec;
int bit=wav_header.wBitsPerSample;
int datablock=wav_header.wBlockAlign;
unsigned char ch[100]; //用来存储wav文件的头信息
rc=snd_pcm_open(&handle, "default", SND_PCM_STREAM_PLAYBACK, 0);
if(rc<0)
{
perror("\nopen PCM device failed:");
exit(1);
}
snd_pcm_hw_params_alloca(¶ms); //分配params结构体
if(rc<0)
{
perror("\nsnd_pcm_hw_params_alloca:");
exit(1);
}
rc=snd_pcm_hw_params_any(handle, params);//初始化params
if(rc<0)
{
perror("\nsnd_pcm_hw_params_any:");
exit(1);
}
rc=snd_pcm_hw_params_set_access(handle, params, SND_PCM_ACCESS_RW_INTERLEAVED); //初始化访问权限
if(rc<0)
{
perror("\nsed_pcm_hw_set_access:");
exit(1);
}
//采样位数
switch(bit/8)
{
case 1:snd_pcm_hw_params_set_format(handle, params, SND_PCM_FORMAT_U8);
break ;
case 2:snd_pcm_hw_params_set_format(handle, params, SND_PCM_FORMAT_S16_LE);
break ;
case 3:snd_pcm_hw_params_set_format(handle, params, SND_PCM_FORMAT_S24_LE);
break ;
}
rc=snd_pcm_hw_params_set_channels(handle, params, channels); //设置声道,1表示单声>道，2表示立体声
if(rc<0)
{
perror("\nsnd_pcm_hw_params_set_channels:");
exit(1);
}
val = frequency;
rc=snd_pcm_hw_params_set_rate_near(handle, params, &val, &dir); //设置>频率
if(rc<0)
{
perror("\nsnd_pcm_hw_params_set_rate_near:");
exit(1);
}
rc = snd_pcm_hw_params(handle, params);
if(rc<0)
{
perror("\nsnd_pcm_hw_params: ");
exit(1);
}
rc=snd_pcm_hw_params_get_period_size(params, &frames, &dir); /*获取周期
长度*/
if(rc<0)
{
perror("\nsnd_pcm_hw_params_get_period_size:");
exit(1);
}
size = frames * datablock; /*4 代表数据快长度*/
buffer =(char*)malloc(size);
fseek(fp,58,SEEK_SET); //定位歌曲到数据区
while (1)
{
memset(buffer,0,sizeof(buffer));
ret = fread(buffer, 1, size, fp);
if(ret == 0)
{
printf("歌曲写入结束\n");
break;
}
else if (ret != size)
{
}
// 写音频数据到PCM设备
while(ret = snd_pcm_writei(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(handle);
}
else if (ret < 0)
{
fprintf(stderr,
"error from writei: %s\n",
snd_strerror(ret));
}
}
}
snd_pcm_drain(handle);
snd_pcm_close(handle);
free(buffer);
return 0;
}
