[alsa-devel] reading 1 second of audio at a time

[folkert]

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) {
        }

        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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