2010/6/22 folkert folkert@vanheusden.com

Hi,

Am trying to achieve something trivial: reading 1 second of audio at a time, but something goes wrong:

Sound 1277148008.835094 Sound 1277148008.838224 Sound 1277148010.834839 Sound 1277148010.838001 Sound 1277148012.834523 Sound 1277148012.837580 Sound 1277148014.835240 Sound 1277148014.838333

As you can see; audio is returned for 2 seconds, then it sleeps 2 secondsn, then 2 seconds of audio, etc.

What I do is:

   if (snd_pcm_hw_params_set_access(pcm_handle, hwparams,

SND_PCM_ACCESS_RW_INTERLEAVED) < 0) { }

   if (snd_pcm_hw_params_set_format(pcm_handle, hwparams,

SND_PCM_FORMAT_S16_LE) < 0) { }

   exact_rate = 44100;
   if (snd_pcm_hw_params_set_rate_near(pcm_handle, hwparams,

&exact_rate, 0) < 0) { error_exit("Error setting rate.\n"); } if (*rate != exact_rate) { fprintf(stderr, "The rate %d Hz is not supported by your hardware.\n ==> Using %d Hz instead.\n", *rate, exact_rate); *rate = exact_rate; }

   if (snd_pcm_hw_params_set_channels(pcm_handle, hwparams, 2) < 0) { }

   int periods = 2;
   if (snd_pcm_hw_params_set_periods(pcm_handle, hwparams, periods, 0)

< 0) { }

   if (snd_pcm_hw_params_set_buffer_size(pcm_handle, hwparams,

exact_rate * 2 * n_channels) < 0) { }

buffer_size is actually no of samples , exact_rate*2*n_channels seem to be buffer_bytes

Have you checked whether hardware driver support exactly 1 second buffer ?

since the most common HDA , you cannot get exactlyy 1 second buffer because period_size is multiple of 128 bytes

   if (snd_pcm_hw_params(pcm_handle, hwparams) < 0) {
   }

   return pcm_handle;

}

void get_audio_1s(snd_pcm_t *pcm_handle, short *buffer, int rate, int channels) { int samples = channels * rate, index = 0;

   while(samples > 0)
   {
           int cur = samples, pcmreturn;

           while ((pcmreturn = snd_pcm_readi(pcm_handle,

&buffer[index], cur)) < 0) { snd_pcm_prepare(pcm_handle); printf(" underrun\n"); }

           index += pcmreturn;
           samples -= pcmreturn;
   }

}

So I call this get_audio_1s() with the samplerate (44100) and the number of channels (2). Then it seems to return the first second at once, then the second second of audio too, then sleeps for 2 seconds(!) and then repeats.

Folkert van Heusden

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