[alsa-devel] Application: Regd ALSA playback

19 May 2011


      Hi,
I am new to ALSA and trying to play a wav file through ALSA by referring the
sample code.
It is a stereo, 44100Hz, 16 bit little endian file.
It is not properly playing the file.
I suspect that the frames parameter might be wrong.
Below is the source code.
Could any one give pointers on this.
long loops;
  int rc;
  int size;
  snd_pcm_t *handle;
  snd_pcm_hw_params_t *params;
  unsigned int val;
  int dir;
  snd_pcm_uframes_t frames;
  char *buffer;
/* Open PCM device for playback. */
  rc = snd_pcm_open(&handle, "default",
                    SND_PCM_STREAM_PLAYBACK, 0);
  if (rc < 0) {
    fprintf(stderr,
            "unable to open pcm device: %s\n",
            snd_strerror(rc));
    exit(1);
  }
/* Allocate a hardware parameters object. */
  snd_pcm_hw_params_alloca(&params);
/* Fill it in with default values. */
  snd_pcm_hw_params_any(handle, params);
/* Set the desired hardware parameters. */
/* Interleaved mode */
  snd_pcm_hw_params_set_access(handle, params,
                      SND_PCM_ACCESS_RW_INTERLEAVED);
/* Signed 16-bit little-endian format */
  snd_pcm_hw_params_set_format(handle, params,
                              SND_PCM_FORMAT_S16_LE);
/* Two channels (stereo) */
  snd_pcm_hw_params_set_channels(handle, params, 2);
/* 44100 bits/second sampling rate (CD quality) */
  val = 44100;
  snd_pcm_hw_params_set_rate_near(handle, params,
                                  &val, &dir);
/* Set period size to 32 frames. */
  frames = 44100;
  snd_pcm_hw_params_set_period_size_near(handle,
                              params, &frames, &dir);
/* Write the parameters to the driver */
  rc = snd_pcm_hw_params(handle, params);
  if (rc < 0) {
    fprintf(stderr,
            "unable to set hw parameters: %s\n",
            snd_strerror(rc));
    exit(1);
  }
/* Use a buffer large enough to hold one period */
  snd_pcm_hw_params_get_period_size(params, &frames,
                                    &dir);
  printf("get period_size: %d\n",frames);
  size = frames * 4 ; /* 2 bytes/sample, 2 channels */
  printf("Size:%d\n",size);
  buffer = (char *) malloc(size);
/* We want to loop for 2 seconds */
  snd_pcm_hw_params_get_period_time(params,
                                    &val, &dir);
  printf("period time: %d\n",val);
  /* 2 seconds in microseconds divided by
   * period time */
  loops = 3000000 / val;
  printf("loops: %d\n",loops);
FILE *fp;
  int file;
fp = fopen("ring-1.wav", "rb");
  if (!fp) {
     printf("file open failure\n");
     return NULL;
  }
  printf("file open success\n");
while (loops > 0) {
    loops--;
    //rc = read(0, buffer, size);
    rc = fread(buffer, sizeof(unsigned char), frames, fp);
      printf("bytes read: %d\n", rc);
    if (rc == 0) {
      printf("end of file on input\n");
      break;
    } else if (rc != size) {
      fprintf(stderr,
              "short read: read %d bytes\n", rc);
    }
    rc = snd_pcm_writei(handle, buffer, frames);
    if (rc == -EPIPE) {
      /* EPIPE means underrun */
      fprintf(stderr, "underrun occurred\n");
      snd_pcm_prepare(handle);
    } else if (rc < 0) {
      fprintf(stderr,
              "error from writei: %s\n",
              snd_strerror(rc));
    }  else if (rc != (int)frames) {
      fprintf(stderr,
              "short write, write %d frames\n", rc);
    }
  }
snd_pcm_drain(handle);
  snd_pcm_close(handle);
  free(buffer);
  fclose(fp);
  return 0;
}
Thanks & Regards,
Thilaga