simple_alsa_test.c

#include <alsa/asoundlib.h>
#include <stdio.h>

#define PCM_DEVICE "hw:0,0"

int main(int argc, char **argv) {
    unsigned int pcm, tmp, dir;
    int rate, channels, seconds;
    snd_pcm_t *pcm_handle;
    snd_pcm_hw_params_t *params;
    snd_pcm_uframes_t frames;
    char *buff;
    int buff_size, loops;
    FILE* fp;

    if (argc != 2) {
        printf("Usage: %s <filename>\n", argv[0]);
        return -1;
    }

    rate     = 44100;
    channels = 2;

    // file open
    fp = fopen(argv[1], "r");
    if(!fp) {
        printf("ERROR: Can't open \"%s\"\n", argv[1]);
        return -1;
    }

    /* Open the PCM device in playback mode */
    if (pcm = snd_pcm_open(&pcm_handle, PCM_DEVICE,
                SND_PCM_STREAM_PLAYBACK, 0) < 0)
        printf("ERROR: Can't open \"%s\" PCM device. %s\n",
                PCM_DEVICE, snd_strerror(pcm));

    /* Allocate parameters object and fill it with default values*/
    snd_pcm_hw_params_alloca(&params);
    snd_pcm_hw_params_any(pcm_handle, params);

    /* Set parameters */
    if (pcm = snd_pcm_hw_params_set_access(pcm_handle, params,
                SND_PCM_ACCESS_RW_INTERLEAVED) < 0)
        printf("ERROR: Can't set interleaved mode. %s\n", snd_strerror(pcm));

    if (pcm = snd_pcm_hw_params_set_format(pcm_handle, params,
                SND_PCM_FORMAT_S16_LE) < 0)
        printf("ERROR: Can't set format. %s\n", snd_strerror(pcm));

    if (pcm = snd_pcm_hw_params_set_channels(pcm_handle, params, channels) < 0)
        printf("ERROR: Can't set channels number. %s\n", snd_strerror(pcm));

    if (pcm = snd_pcm_hw_params_set_rate_near(pcm_handle, params, &rate, 0) < 0)
        printf("ERROR: Can't set rate. %s\n", snd_strerror(pcm));

    /* Write parameters */
    if (pcm = snd_pcm_hw_params(pcm_handle, params) < 0)
        printf("ERROR: Can't set harware parameters. %s\n", snd_strerror(pcm));

    /* Resume information */
    printf("PCM name: '%s'\n", snd_pcm_name(pcm_handle));

    printf("PCM state: %s\n", snd_pcm_state_name(snd_pcm_state(pcm_handle)));

    snd_pcm_hw_params_get_channels(params, &tmp);
    printf("channels: %i ", tmp);

    if (tmp == 1)
        printf("(mono)\n");
    else if (tmp == 2)
        printf("(stereo)\n");

    snd_pcm_hw_params_get_rate(params, &tmp, 0);
    printf("rate: %d bps\n", tmp);

    /* Allocate buffer to hold single period */
    snd_pcm_hw_params_get_period_size(params, &frames, 0);

    buff_size = frames * channels * 2 /* 2 -> sample size */;
    buff = (char *) malloc(buff_size);

    snd_pcm_hw_params_get_period_time(params, &tmp, NULL);

    while(!feof(fp)) {
        if(pcm = fread(buff, buff_size, 1, fp) == 0) {
            printf("Early end of file.\n");
            return 0;
        }
        if (pcm = snd_pcm_writei(pcm_handle, buff, frames) == -EPIPE) {
            printf("XRUN.\n");
            snd_pcm_prepare(pcm_handle);
        } else if (pcm < 0) {
            printf("ERROR. Can't write to PCM device. %s\n", snd_strerror(pcm));
        }
    }

    snd_pcm_drain(pcm_handle);
    snd_pcm_close(pcm_handle);
    free(buff);
    fclose(fp);

    return 0;
}

1. playback 모드로 열고 (snd_pcm_open)
2. 세팅
   1. 열기 (snd_pcm_hw_params_alloca, snd_pcm_hw_params_any)
   2. 세팅에 r/w 알려주구요 (snd_pcm_hw_params_set_access)
   3. 세팅에 비트레이트 (snd_pcm_hw_params_set_format)
   4. 샘플레이트 (snd_pcm_hw_params_set_rate_near)
   5. 채널 수 알려준다음 (snd_pcm_hw_params_set_channels)
   6. 설정된 거 적용 (snd_pcm_hw_params)
3. 설정 잘 적용됬는지 확인도 해보구요 (snd_pcm_hw_params_get_period_size, snd_pcm_hw_params_get_period_time)
4. 음원 재생 (snd_pcm_writei)
5. 끝나면 뒷정리 (snd_pcm_hw_params_free, snd_pcm_drain, snd_pcm_close)