Wav files are played by alsa at a faster tempo. Is there a way to fix the tempo

58 Views Asked by At

I am trying to play audio files programmatically using alsa library. My platform is Linux and my end product will be an embedded board. I have modified the code found here https://gist.github.com/ghedo/963382/ as my stating point. Instead of playing from the stdin in the code from above link, I will be using wav files.

The sample wave files played are from the location https://www2.cs.uic.edu/~i101/SoundFiles/ e.g https://www2.cs.uic.edu/~i101/SoundFiles/PinkPanther30.wav

My code

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

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;
    int fd;

    if (argc < 5) {
        printf("Usage: %s <sample_rate> <channels> <seconds> <file-wav> <interface>\n", argv[0]);
        return -1;
    }

    fd = open(argv[4], O_RDONLY, 0);
    if (fd < 0) {
        printf("File not found %s\n", argv[4]);
        return 0;
    }

    lseek(fd, 44, SEEK_SET);

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

    /* Open the PCM device in playback mode */
    if (pcm = snd_pcm_open(&pcm_handle, argv[5], SND_PCM_STREAM_PLAYBACK, 0) < 0)
        printf("ERROR: Can't open \"%s\" PCM device. %s\n", argv[5], 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);

    printf("seconds: %d\n", seconds);

    /* 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 (pcm = read(fd, buff, buff_size) > 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));
        }
        usleep(10);
    }

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

    return 0;
}

The major changes in the code are

fd = open(argv[4], O_RDONLY, 0);
if (fd < 0) {
    printf("File not found %s\n", argv[4]);
    return 0;
}

lseek(fd, 44, SEEK_SET);

Lseek was suggested in the comments

The issue: I find that the file is played faster, i.e. when I play the same files with aplay this code plays the wav file at a different tempo.

I have compared the code from aplay, the playback code as shown here https://github.com/alsa-project/alsa-utils/blob/master/aplay/aplay.c#L3032 and could not find any drastic difference.

I have also tried the code from this question ALSA: wav file playing and find that the file is played faster that the normal tempo.

Could any one point out what am i missing here?

0

There are 0 best solutions below