省运会研究中心成立 智力打造“扬州模板”

今天对收到的米尔-STM32MP257开发板做音频播放测试，是实现基于alsa的音频播放与采集。本文来实现基于alsa播放wav格式pcm音频。

1. 实现

   新建alsa_play_wav.c文件。
   2.1 wav 解析

   Wav解析与添加头代码如下

   #include <stdint.h>
   #include <stdio.h>
   #include <string.h>
   /* WAV解析 */
   #define CHUNK_RIFF "RIFF"
   #define CHUNK_WAVE "WAVE"
   #define CHUNK_FMT "fmt "
   #define CHUNK_DATA "data"
   typedef struct
   {    uint32_t off;    uint32_t chunksize;    uint16_t audioformat;    uint16_t numchannels;    uint32_t samplerate;    uint32_t byterate;    uint16_t blockalign;    uint16_t bitspersample;    uint32_t datasize;}wav_t;static int wav_decode_head(uint8_t* buffer, wav_t* wav)
   {    uint8_t* p = buffer;    uint32_t chunksize;    uint32_t subchunksize;    if(0 != memcmp(p,CHUNK_RIFF,4))
       {        return -1;
       }    p += 4;
       chunksize = (uint32_t)p[0] | ((uint32_t)p[1]<<8) | ((uint32_t)p[2]<<16) | ((uint32_t)p[3]<<24);
       wav->chunksize = chunksize;    p += 4;
       if(0 != memcmp(p,CHUNK_WAVE,4))
       {        return -2;
       }    p += 4;
       do
       {        if(0 == memcmp(p,CHUNK_FMT,4))
           {            p += 4;
               subchunksize = (uint32_t)p[0] | ((uint32_t)p[1]<<8) | ((uint32_t)p[2]<<16) | ((uint32_t)p[3]<<24);
               p += 4;
               /* 解析参数 */
               wav->audioformat = (uint16_t)p[0] | ((uint16_t)p[1]<<8);
               if((wav->audioformat == 0x0001) || (wav->audioformat == 0xFFFE))
               {                p += 2;
                   wav->numchannels = (uint16_t)p[0] | ((uint16_t)p[1]<<8);
                   p += 2;
                   wav->samplerate = (uint32_t)p[0] | ((uint32_t)p[1]<<8) | ((uint32_t)p[2]<<16) | ((uint32_t)p[3]<<24);
                   p += 4;
                   wav->byterate = (uint32_t)p[0] | ((uint32_t)p[1]<<8) | ((uint32_t)p[2]<<16) | ((uint32_t)p[3]<<24);
                   p += 4;
                   wav->blockalign = (uint16_t)p[0] | ((uint16_t)p[1]<<8);
                   p += 2;
                   wav ->bitspersample = (uint16_t)p[0] | ((uint16_t)p[1]<<8);
                   p += 2;
                   if(subchunksize >16)
                   {                    /* 有ext区域 */
                       uint16_t cbsize = (uint16_t)p[0] | ((uint16_t)p[1]<<8);
                       p += 2;
                       if(cbsize > 0)
                       {                        /* ext数据 2字节有效bits wValidBitsPerSample ，4字节dwChannelMask 16字节SubFormat */
                           p += 2;
                           p += 4;
                           /* 比对subformat */
                           p += 16;       
                       }                }            }            else
               {                p += subchunksize;            }        }        else if(0 == memcmp(p,CHUNK_DATA,4))
           {            p += 4;
               subchunksize = (uint32_t)p[0] | ((uint32_t)p[1]<<8) | ((uint32_t)p[2]<<16) | ((uint32_t)p[3]<<24);
               wav->datasize = subchunksize;            p += 4;
               wav->off = (uint32_t)(p- buffer);            return 0;
           }        else
           {            p += 4;
               subchunksize = (uint32_t)p[0] | ((uint32_t)p[1]<<8) | ((uint32_t)p[2]<<16) | ((uint32_t)p[3]<<24);
               p += 4;
               p += subchunksize;        }    }while((uint32_t)(p - buffer) < (chunksize + 8));
       return -3;
   }/* 填充44字节的wav头 */
   static void wav_fill_head(uint8_t* buffer, int samples, int chnum, int freq)
   {    /*
        * 添加wav头信息
        */
       uint32_t chunksize = 44-8+samples*chnum*16/8;
       uint8_t* p = (uint8_t*)buffer;    uint32_t bps = freq*chnum*16/8;
       uint32_t datalen = samples*chnum*16/8;
       p[0] = 'R';
       p[1] = 'I';
       p[2] = 'F';
       p[3] = 'F';
       p[4] = chunksize & 0xFF;
       p[5] = (chunksize>>8) & 0xFF;
       p[6] = (chunksize>>16) & 0xFF;
       p[7] = (chunksize>>24) & 0xFF;
       p[8] = 'W';
       p[9] = 'A';
       p[10] = 'V';
       p[11] = 'E';
       p[12] = 'f';
       p[13] = 'm';
       p[14] = 't';
       p[15] = ' ';
       p[16] = 16;  /* Subchunk1Size */
       p[17] = 0;
       p[18] = 0;
       p[19] = 0;
       p[20] = 1;  /* PCM */
       p[21] = 0;
       p[22] = chnum; /* 通道数 */
       p[23] = 0;
       p[24] = freq & 0xFF;
       p[25] = (freq>>8) & 0xFF;
       p[26] = (freq>>16) & 0xFF;
       p[27] = (freq>>24) & 0xFF; 
       p[28] = bps & 0xFF;      /* ByteRate */
       p[29] = (bps>>8) & 0xFF;
       p[30] = (bps>>16) & 0xFF;
       p[31] = (bps>>24) & 0xFF; 
       p[32] = chnum*16/8; /* BlockAlign */
       p[33] = 0;
       p[34] = 16;  /* BitsPerSample */
       p[35] = 0;
       p[36] = 'd';
       p[37] = 'a';
       p[38] = 't';
       p[39] = 'a';
       p[40] = datalen & 0xFF;
       p[41] = (datalen>>8) & 0xFF;
       p[42] = (datalen>>16) & 0xFF;
       p[43] = (datalen>>24) & 0xFF; 
   }void wav_print(wav_t* wav)
   {   printf("off:%d\\r\\n",wav->off); 
      printf("chunksize:%d\\r\\n",wav->chunksize); 
      printf("audioformat:%d\\r\\n",wav->audioformat); 
      printf("numchannels:%d\\r\\n",wav->numchannels); 
      printf("samplerate:%d\\r\\n",wav->samplerate); 
      printf("byterate:%d\\r\\n",wav->byterate); 
      printf("blockalign:%d\\r\\n",wav->blockalign); 
      printf("bitspersample:%d\\r\\n",wav->bitspersample); 
      printf("datasize:%d\\r\\n",wav->datasize); 
   }
   

   2.2 alsa播放

   打开设备与参数初始化

   int alsa_init(char* device, snd_pcm_t **handle, wav_t* wav)
   {    int err;
       if ((err = snd_pcm_open(handle, device, SND_PCM_STREAM_PLAYBACK, 0)) < 0) {  /* 最后一个参数0 阻塞模式 1非阻塞模式 */
           printf("Playback open error: %s\\n", snd_strerror(err));
           return -1;
       }    snd_pcm_sframes_t frames;    if ((err = snd_pcm_set_params(*handle,
                       SND_PCM_FORMAT_S16_LE,                    SND_PCM_ACCESS_RW_INTERLEAVED,                    wav->numchannels,                    wav->samplerate,                    0,
                       100000)) < 0) {   /* 0.5sec */
           printf("Playback open error: %s\\n", snd_strerror(err));
           snd_pcm_close(*handle);        return -2;
       }	snd_pcm_hw_params_t *hwparams = NULL;
   	snd_pcm_hw_params_malloc(&hwparams);
   	snd_pcm_hw_params_any(*handle, hwparams);
   	snd_pcm_hw_params_set_access(*handle, hwparams, SND_PCM_ACCESS_RW_INTERLEAVED);
   	snd_pcm_hw_params_set_format(*handle, hwparams,SND_PCM_FORMAT_S16_LE);
   	snd_pcm_hw_params_set_channels(*handle, hwparams,wav->numchannels);
   	snd_pcm_hw_params_set_rate(*handle, hwparams,wav->samplerate,0);
   	snd_pcm_hw_params_set_period_size(*handle, hwparams, NN, 0);
   	snd_pcm_hw_params_set_buffer_size(*handle, hwparams, 4*NN);
   	snd_pcm_hw_params(*handle, hwparams);
   	snd_pcm_hw_params_free(hwparams);
       return 0;
   }
   

   播放：

   int alsa_play(snd_pcm_t *handle, const void* buffer, size_t size)
   {    snd_pcm_sframes_t frames;    frames = snd_pcm_writei(handle, buffer, (snd_pcm_uframes_t)size);  /* 注意这里的size为frames即点数 而不是字节大小 */
       if (frames < 0){
           frames = snd_pcm_recover(handle, frames, 0);
           printf("snd_pcm_recover: %s\\n", snd_strerror(frames));
       }    if (frames < 0) {
           printf("snd_pcm_writei failed: %s\\n", snd_strerror(frames));
           return -1;
       }    if (frames > 0 && frames < (long)sizeof(buffer)){
           printf("Short write (expected %li, wrote %li)\\n", (long)sizeof(buffer), frames);
           return -2;
       }    return 0;
   }
   

   完成关闭：

   int alsa_deinit(snd_pcm_t *handle)
   {    int err;
       /* pass the remaining samples, otherwise they're dropped in close */
       err = snd_pcm_drain(handle);    if (err < 0){
           printf("snd_pcm_drain failed: %s\\n", snd_strerror(err));
       }    snd_pcm_close(handle);    return 0;
   }
   

   2.3 读取wav文件进行播放

   #include <alsa/asoundlib.h>
   #define NN 128
   #define MAX_CH 2
   int main(int argc, char* argv[])
   {    snd_pcm_t *handle = NULL;    int res;
       FILE *wav_fd;    int16_t wav_buf[NN*MAX_CH];    uint8_t wav_head_buf[128]; /* 输入wav文件头缓存 */
       wav_t wav;    int samps;  /* 采样点数 */
       int times;    /* 读取次数 */
       int sampleRate;
       if(argc != 3){
           printf("usage:alsa_play_wav dev wav\\r\\n");
           return -1;
       }    wav_fd = fopen(argv[2], "rb");
       if(wav_fd < 0){
           printf("open file %s err\\r\\n",argv[2]);
           return -2;
       }    if(sizeof(wav_head_buf) != fread(wav_head_buf, 1, sizeof(wav_head_buf), wav_fd)){
           printf("read file %s err\\r\\n",argv[2]);
           fclose(wav_fd);        return -3;
       }    if(0 != (res=wav_decode_head(wav_head_buf, &wav))){
           printf("decode file %s err %d\\r\\n",argv[2],res);
           fclose(wav_fd);        return -4;
       }    printf("[wav]\\r\\n");
       wav_print(&wav);    samps = wav.datasize;    samps /= wav.blockalign;  /* 采样点数 =  数据大小 除以 blockalign */
       printf("\\r\\nsamps:%d\\r\\n",samps);
       sampleRate = wav.samplerate;    res = alsa_init(argv[1], &handle, &wav);
       if(res != 0){
           fclose(wav_fd);        printf("alsa_init err\\r\\n");
           return -5;
       }    times = samps / NN;   /* 一次读取NN个点,读取times次 */
       fseek(wav_fd,wav.off,SEEK_SET);    for(int i=0; i<times; i++)
       {       if(NN*wav.numchannels != fread(wav_buf, sizeof(int16_t), NN*wav.numchannels, wav_fd)){
               printf("read file %s err\\r\\n",argv[2]);
               fclose(wav_fd);            alsa_deinit(handle);            return -6;
          }       if(alsa_play(handle, wav_buf, NN) < 0){
           printf("play %s err\\r\\n");
           fclose(wav_fd);        alsa_deinit(handle);        return -7;
          }    }    fclose(wav_fd);    alsa_deinit(handle);    return 0;
   }
   

2. 测试

   编译

   source /opt/st/myd-ld25x/4.2.4-snapshot/environment-setup-cortexa35-ostl-linux

   $CC alsa_play_wav.c -o alsa_play_wav -lasound

   导出到windows下

   cp alsa_play_wav /mnt/d

   导入到开发板
   

chmod +x alsa_play_wav

准备wav文件

下载一个mp3音乐，使用ffmpeg转为wav

.\ffmpeg-7.1.1-full_build\bin\ffmpeg.exe -i zdcxf.mp3 -ac 1 -ar 16000 -ss 0 -t 20 sp1.wav

.\ffmpeg-7.1.1-full_build\bin\ffmpeg.exe -i zdcxf.mp3 -ac 2 -ar 16000 -ss 0 -t 20 sp2.wav

导入测试wav文件

1. 测试

   ./alsa_play_wav default sp1.wav

   ./alsa_play_wav default sp2.wav

2. 总结

米尔-STM32MP257开发板按以上代码就可以实现了播放wav音频。(文中测试代码来自网络)