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.
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#include<stdio.h>
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#include<stdlib.h>
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#include <string.h>
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#include <alsa/asoundlib.h>
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struct WAV_HEADER
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{
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char rld[4]; //riff 标志符号
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int rLen;
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char wld[4]; //格式类型(wave)
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char fld[4]; //"fmt"
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int fLen; //sizeof(wave format matex)
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short wFormatTag; //编码格式
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short wChannels; //声道数
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int nSamplesPersec ; //采样频率
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int nAvgBitsPerSample;//WAVE文件采样大小
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short wBlockAlign; //块对齐
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short wBitsPerSample; //WAVE文件采样大小
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char dld[4]; //”data“
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int wSampleLength; //音频数据的大小
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} wav_header;
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int set_pcm_play(FILE *fp);
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int main(int argc,char *argv[])
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{
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if(argc!=2)
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{
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printf("Usage:wav-player+wav file name\n");
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exit(1);
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}
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int nread;
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FILE *fp;
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fp=fopen(argv[1],"rb");
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if(fp==NULL)
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{
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perror("open file failed:\n");
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exit(1);
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}
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nread=fread(&wav_header,1,sizeof(wav_header),fp);
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printf("nread=%d\n",nread);
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//printf("RIFF 标志%s\n",wav_header.rld);
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printf("文件大小rLen:%d\n",wav_header.rLen);
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//printf("wld=%s\n",wav_header.wld);
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//printf("fld=%s\n",wav_header.fld);
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// printf("fLen=%d\n",wav_header.fLen);
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//printf("wFormatTag=%d\n",wav_header.wFormatTag);
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printf("声道数:%d\n",wav_header.wChannels);
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printf("采样频率:%d\n",wav_header.nSamplesPersec);
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//printf("nAvgBitsPerSample=%d\n",wav_header.nAvgBitsPerSample);
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//printf("wBlockAlign=%d\n",wav_header.wBlockAlign);
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printf("采样的位数:%d\n",wav_header.wBitsPerSample);
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// printf("data=%s\n",wav_header.dld);
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printf("wSampleLength=%d\n",wav_header.wSampleLength);
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set_pcm_play(fp);
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return 0;
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}
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int set_pcm_play(FILE *fp)
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{
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int rc;
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int ret;
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int size;
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snd_pcm_t* handle; //PCI设备句柄
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snd_pcm_hw_params_t* params;//硬件信息和PCM流配置
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unsigned int val;
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int dir=0;
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snd_pcm_uframes_t frames;
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char *buffer;
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int channels=wav_header.wChannels;
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int frequency=wav_header.nSamplesPersec;
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int bit=wav_header.wBitsPerSample;
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int datablock=wav_header.wBlockAlign;
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unsigned char ch[100]; //用来存储wav文件的头信息
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rc=snd_pcm_open(&handle, "default", SND_PCM_STREAM_PLAYBACK, 0);
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if(rc<0)
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{
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perror("\nopen PCM device failed:");
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exit(1);
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}
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snd_pcm_hw_params_alloca(¶ms); //分配params结构体
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if(rc<0)
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{
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perror("\nsnd_pcm_hw_params_alloca:");
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exit(1);
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}
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rc=snd_pcm_hw_params_any(handle, params);//初始化params
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if(rc<0)
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{
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perror("\nsnd_pcm_hw_params_any:");
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exit(1);
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}
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rc=snd_pcm_hw_params_set_access(handle, params, SND_PCM_ACCESS_RW_INTERLEAVED); //初始化访问权限
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if(rc<0)
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{
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perror("\nsed_pcm_hw_set_access:");
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exit(1);
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}
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//采样位数
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switch(bit/8)
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{
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case 1:snd_pcm_hw_params_set_format(handle, params, SND_PCM_FORMAT_U8);
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break ;
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case 2:snd_pcm_hw_params_set_format(handle, params, SND_PCM_FORMAT_S16_LE);
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break ;
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case 3:snd_pcm_hw_params_set_format(handle, params, SND_PCM_FORMAT_S24_LE);
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break ;
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}
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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
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if(rc<0)
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{
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perror("\nsnd_pcm_hw_params_set_channels:");
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exit(1);
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}
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val = frequency;
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rc=snd_pcm_hw_params_set_rate_near(handle, params, &val, &dir); //设置>频率
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if(rc<0)
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{
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perror("\nsnd_pcm_hw_params_set_rate_near:");
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exit(1);
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}
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rc = snd_pcm_hw_params(handle, params);
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if(rc<0)
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{
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perror("\nsnd_pcm_hw_params: ");
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exit(1);
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}
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rc=snd_pcm_hw_params_get_period_size(params, &frames, &dir); /*获取周期
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长度*/
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if(rc<0)
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{
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perror("\nsnd_pcm_hw_params_get_period_size:");
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exit(1);
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}
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size = frames * datablock; /*4 代表数据快长度*/
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buffer =(char*)malloc(size);
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fseek(fp,58,SEEK_SET); //定位歌曲到数据区
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while (1)
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{
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memset(buffer,0,sizeof(buffer));
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ret = fread(buffer, 1, size, fp);
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if(ret == 0)
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{
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printf("歌曲写入结束\n");
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break;
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}
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else if (ret != size)
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{
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}
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// 写音频数据到PCM设备
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while(ret = snd_pcm_writei(handle, buffer, frames)<0)
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{
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usleep(2000);
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if (ret == -EPIPE)
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{
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/* EPIPE means underrun */
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fprintf(stderr, "underrun occurred\n");
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//完成硬件参数设置,使设备准备好
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snd_pcm_prepare(handle);
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}
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else if (ret < 0)
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{
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fprintf(stderr,
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"error from writei: %s\n",
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snd_strerror(ret));
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}
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}
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}
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snd_pcm_drain(handle);
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snd_pcm_close(handle);
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free(buffer);
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return 0;
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}
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