1

为什么下面的程序会为 snd_pcm_hw_params_set_period_size()、snd_pcm_hw_params_set_buffer_size() 和 snd_pcm_hw_params_set_rate() 发出错误？如果我将 SAMPLES 的值提高到 768，它只会向 snd_pcm_hw_params_set_rate() 发出错误。值“512”在这里很重要，因为我将一个程序移植到 ALSA，它使用 512 个样本作为其缓冲区（或 256 帧）的大小。

错误消息只是“无效参数” - 我知道，它很模糊。

#include <stdlib.h>
#include <stdint.h>
#include <alsa/asoundlib.h>

#define STEREO              2
#define SIXTEENBITS         2
#define SAMPLES           512
#define PERIODS             2
#define SAMPLERATE      11025

void snd_error_checker(int error, char *function_name)
{
    if (error)
    {
        printf("Error (%s): %s\n", function_name, snd_strerror(error));
        // exit(EXIT_FAILURE);
    }
}

int main(void)
{
    snd_pcm_t *handle;
    uint32_t channels                   = STEREO;
    uint32_t sample_size                = SIXTEENBITS;
    uint32_t frame_size                 = sample_size * channels;
    snd_pcm_uframes_t frames            = SAMPLES / frame_size;
    snd_pcm_uframes_t frames_per_period = frames / PERIODS;
    int32_t dir = 0; // No idea what this does.
    snd_pcm_hw_params_t *params;
    int error;

    error = snd_pcm_open(&handle, "default", SND_PCM_STREAM_PLAYBACK, 0);
    snd_error_checker(error, "snd_pcm_open()");
    snd_pcm_hw_params_malloc(&params);
    error = snd_pcm_hw_params_any(handle, params);
    snd_error_checker(error, "snd_pcm_hw_params_any()");
    error = snd_pcm_hw_params_set_period_size(handle, params, frames_per_period, dir);
    snd_error_checker(error, "snd_pcm_hw_params_set_period_size()");
    error = snd_pcm_hw_params_set_periods(handle, params, PERIODS, dir);
    snd_error_checker(error, "snd_pcm_hw_params_set_periods()");
    error = snd_pcm_hw_params_set_buffer_size(handle, params, frames);
    snd_error_checker(error, "snd_pcm_hw_params_set_buffer_size()");
    error = snd_pcm_hw_params_set_rate(handle, params, SAMPLERATE, dir);
    snd_error_checker(error, "snd_pcm_hw_params_set_rate()");
    error = snd_pcm_hw_params_set_access(handle, params, SND_PCM_ACCESS_RW_INTERLEAVED);
    snd_error_checker(error, "snd_pcm_hw_params_set_access()");
    error = snd_pcm_hw_params_set_channels(handle, params, STEREO);
    snd_error_checker(error, "snd_pcm_hw_params_set_channels()");
    error = snd_pcm_hw_params_set_format(handle, params, SND_PCM_FORMAT_S16_LE);
    snd_error_checker(error, "snd_pcm_hw_params_set_format()");
    error = snd_pcm_hw_params(handle, params);
    snd_error_checker(error, "snd_pcm_hw_params()");

    snd_pcm_drain(handle);
    snd_pcm_close(handle);
    exit(EXIT_SUCCESS);
}
4

1 回答 1

3

硬件参数取决于硬件的能力。您可以使用 get_xxx_min/max 函数来确定硬件支持什么，或者调用 set_xxx_near 来选择最接近的实际支持的值。

在任何情况下，硬件缓冲区大小都不需要与应用程序的缓冲区大小相同。

于 2020-06-26T07:25:40.643 回答