Alsa，无法连续播放同一曲目两次

Question

我开发了一些代码来播放音频（波形文件）。当我尝试播放同一个文件两次时，第一次播放正常，但第二次播放时总是失败。

下面是一次性音频初始化函数

/* PCM interface objects */
static snd_pcm_t *pcm_handle;
static snd_pcm_uframes_t frames;
static int rate = 44100, channels = 2;

void audio_init(void)
{
    snd_pcm_hw_params_t *params;
    unsigned int pcm = 0;

    /* 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);

    /* Interleaved mode */
    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));

    /* Signed 16 bit little-endian format */
    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));

    /* Two channels, stereo */
    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));

    /* 44100 bits/second sampling rate (CD quality) */
    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 to the driver */
    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)));

    int tmp = 0;
    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 large enough buffer to hold single period (No. of samples) */
    snd_pcm_hw_params_get_period_size(params, &frames, 0);
    printf("period size = %d frames\n", (int)frames);

    /* Get the period time */
    snd_pcm_hw_params_get_period_time(params, &tmp, NULL);
    printf("period time = %d us\n", tmp);

    audio_playTrack(AUDIO_HOMING_TRACK);
    sleep(1);
    printf("PCM state: %s\n", snd_pcm_state_name(snd_pcm_state(pcm_handle)));
    audio_playTrack(AUDIO_ARRIVE_TRACK);
    sleep(1);
    printf("PCM state: %s\n", snd_pcm_state_name(snd_pcm_state(pcm_handle)));
}

下面是我在 audio_init( ) 末尾调用两次的函数。

void audio_playTrack(char *audioFile)
{
    short int* buf = NULL;
    int readcount = 0;
    int pcmrc;
    SNDFILE *infile = NULL;
    SF_INFO sfinfo;

    infile = sf_open(audioFile, SFM_READ, &sfinfo);

    printf("\r\n");
    printf("[FILE]Channels      : %d\n", sfinfo.channels);
    printf("[FILE]Sample rate   : %d\n", sfinfo.samplerate);
    printf("[FILE]Sections      : %d\n", sfinfo.sections);
    printf("[FILE]Format        : %d\n", sfinfo.format);
    printf("\r\n");

    printf("+------------------\n");
    printf("### AUDIO BEGIN ###\n");
    printf("+------------------\n\n");
    buf = malloc(frames * sfinfo.channels * sizeof(int));
    while ((readcount = sf_readf_short(infile, buf, frames))>0)
    {
        pcmrc = snd_pcm_writei(pcm_handle, buf, readcount);
        if (pcmrc == -EPIPE)
        {
            printf("Underrun!\n");
            snd_pcm_prepare(pcm_handle);
        }
        else if (pcmrc < 0)
        {
            printf("Error writing to PCM device: %s\n", snd_strerror(pcmrc));
        }
        else if (pcmrc != readcount)
        {
            printf("PCM write differs from PCM read.\n");
        }
    }
    printf("+------------------\n");
    printf("### AUDIO END ###\n");
    printf("+------------------\n\n");
    free(buf);
    sf_close (infile);
}

对第一个 audio_playTrack() 的调用有效。第二个不作为 sf_readf_short returns 0 帧，甚至不进入 while 循环。

我希望能够在代码中随时停止和重新启动音频。谁能帮我理解为什么 sf_readf_short returns 0 和 audio_playTrack() 在第二次调用时失败？

下面是控制台打印。

PCM name: 'default'
PCM state: PREPARED
channels: 2 (stereo)
rate: 44100 bps
period size = 940 frames
period time = 21333 us

[FILE]Channels          : 2
[FILE]Sample rate       : 44100
[FILE]Sections          : 1
[FILE]Format            : 65538

+------------------
### AUDIO BEGIN ###
+------------------

+------------------
### AUDIO END ###
+------------------

PCM state: RUNNING

[FILE]Channels          : 2
[FILE]Sample rate       : 44100
[FILE]Sections          : 1
[FILE]Format            : 65538

+------------------
### AUDIO BEGIN ###
+------------------

Underrun!
+------------------
### AUDIO END ###
+------------------

编辑：从 audio_playTrack( ) 中删除了 snd_pcm_drain( ) 并将 snd_pcm_hw_params_t 参数设为 audio_init( )

的本地参数

Answer 1

两次调用的文件对象 infile 相同。所以你第一次已经到了文件的末尾，那么你第二次尝试播放时，你仍然在文件的末尾。您需要关闭并重新打开文件，或者在尝试再次播放之前倒回到开头。

Alsa，无法连续播放同一曲目两次

Alsa, unable to play the same track twice in sequence

c

alsa

libsndfile