我正在使用 ALSA 库编写 Linux c 应用程序代码来播放 wav 文件。

这是我的示例代码，它打开 wav 文件的文件描述符，并将读取缓冲区从 wav 文件写入声音设备。

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

#define PCM_DEVICE "default"

int main(int argc, char *argv[]) 
{
    unsigned int pcm, tmp, dir;
    int rate, channels, format;
    snd_pcm_t *pcm_handle;
    snd_pcm_hw_params_t *params;
    snd_pcm_uframes_t frames;
    char *buff = NULL;
    int buff_size;
    int readfd, readval = 0;

    if (argc < 4) {
         printf("Usage: %s <sample_rate> <channels> <format> <wav_file>"
              "\nchannels 1 = mono, 2 = stereo "
              "\nformat for (signed 8 bit = 0, unsigned 8 bit = 1, signed 16 bit = 2 LE, signed 16 bit LE = 4)\n",
            argv[0]);
    return -1;
    }

    rate     = atoi(argv[1]);
    channels = atoi(argv[2]);
    format   = atoi(argv[3]);

    /* 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,
                    format) < 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);
    printf("frames: %d\n", (int)frames); 

    buff_size = frames * channels * 2 /* 2 -> sample size */;
    buff = (char *) malloc(buff_size);
    memset(buff, 0, buff_size);

    snd_pcm_hw_params_get_period_time(params, &tmp, NULL);

    readfd = open(argv[4], O_RDONLY);
    if (readfd < 0) {
          perror("wavread");
          exit(1);
    }

    while(readval = read(readfd, buff, buff_size) > 0) {      
         if (pcm = snd_pcm_writei(pcm_handle, buff, frames) == -EPIPE) {
                fprintf(stderr, "Underrun!\n");
                snd_pcm_prepare(pcm_handle);
         } else if (pcm < 0) {
                fprintf(stderr, "Error writing to PCM device: %s\n", snd_strerror(pcm));
        }
    }

    snd_pcm_drain(pcm_handle);
    snd_pcm_close(pcm_handle);
    free(buff);
    return 0;
}

但是，它只播放 wav 文件 30 秒。这种行为的根本原因是什么？

c alsa