我想把一个char*转换成float*。

问题描述 投票:0回答:1

我试图使用ALSA录制音频,并将其传递给处理人员。音频样本的返回是char*转float*。

我尝试了很多解决方案,我想我明白了,这不是一个真正的char缓冲区,而是一个字节缓冲区,但我如何让它成为一个float。

这将返回缓冲区。

const unsigned char* arBuffer(void)
{
    return buffer;
}

我需要把麦克风的输出作为一个浮点数来使用。

 int32_t O_DecodeAudioBuffer(float *audioBuffer, int size, void *oxyingObject)
{
  Core *oxying = (COxyCore*)oxyingObject;

  //Decode audioBuffer to check if begin token is found, we should keep previous buffer to check if token was started in previous
  //var mDecoding > 0 when token has been found, once decoding is finished, mDecoding = 0
  return oxying->mDecoder->DecodeAudioBuffer(audioBuffer, size);
}

我写了一个程序来消耗上面的api。

void* mOxyCore; is declared

然后我试着传递arBuffer(),但没有达到预期的效果。

while(arIsRunning())
    {

        int ret = DecodeAudioBuffer(arBuffer(), arBufferSize(), mCore);
    }

Alsa.I试图使用ALSA录制音频,并将其传递给处理。

/* Use the newer ALSA API */
#define ALSA_PCM_NEW_HW_PARAMS_API

#include <stdlib.h>
#include <alsa/asoundlib.h>
#include <pthread.h>
#include "settings.h"
#include "audiorecorder.h"


pthread_t thr;
pthread_mutex_t mutex;
snd_pcm_t *handle;
snd_pcm_uframes_t frames;
unsigned char* buffer;
BOOL running;
size_t buffersize;


BOOL arIsRunning(void)
{
    return running;
}


void arAcquireBuffer(void)
{
    //printf("Acquired buffer\n");
    pthread_mutex_lock(&mutex);
}


void arReleaseBuffer(void)
{
    //printf("Released buffer\n");
    pthread_mutex_unlock(&mutex);
}


const unsigned char* arBuffer(void)
{
    return buffer;
}


const size_t arBufferSize(void)
{
    return buffersize;
}


void* entry_point(void *arg)
{
    int rc;

    fprintf(stderr, "Listening...\n");

  while (running)
    {
        arAcquireBuffer();
    rc = snd_pcm_readi(handle, buffer, frames);

    //stream to stdout - useful for testing/debugging
    //write(1, buffer, buffersize);
        arReleaseBuffer();

    if (rc == -EPIPE) {
      /* EPIPE means overrun */
      fprintf(stderr, "overrun occurred\n");
      snd_pcm_prepare(handle);
    }
        else if (rc < 0) {
      fprintf(stderr, "error from read: %s\n", snd_strerror(rc));
            running = FALSE;
    }
        else if (rc != (int)frames) {
      fprintf(stderr, "short read, read %d frames\n", rc);
    }
 }

    return NULL;
}



int arInitialise(void)
{
  snd_pcm_hw_params_t *params;
  unsigned int val;
  int rc, dir;

    running = FALSE;

  /* Open PCM device for recording (capture). */
  rc = snd_pcm_open(&handle, RECORDER_DEVICE, SND_PCM_STREAM_CAPTURE, 0);
  if (rc < 0) {
    fprintf(stderr, "unable to open pcm device: %s\n", snd_strerror(rc));
    return rc;
  }
    else
    {
        fprintf(stderr, "Successfully opened default capture device.\n");
    }

  /* Allocate a hardware parameters object. */
  snd_pcm_hw_params_alloca(&params);

  /* Fill it in with default values. */
  snd_pcm_hw_params_any(handle, params);

  /* Set the desired hardware parameters. */

  /* Interleaved mode */
  snd_pcm_hw_params_set_access(handle, params, SND_PCM_ACCESS_RW_INTERLEAVED);

  /* Signed 16-bit little-endian format */
  snd_pcm_hw_params_set_format(handle, params, SND_PCM_FORMAT_S16_LE);
    fprintf(stderr, "Format set to PCM Signed 16bit Little Endian.\n");


  /* Channels */
  snd_pcm_hw_params_set_channels(handle, params, NUM_CHANNELS);
    fprintf(stderr, "Channels set to %d.\n", NUM_CHANNELS);


  /* sampling rate */
  val = SAMPLE_RATE;
  snd_pcm_hw_params_set_rate_near(handle, params, &val, &dir);
    fprintf(stderr, "Samplerate set to %d.\n", val);

  /* Set period to FRAMES_PER_BUFFER frames. */
  frames = FRAMES_PER_BUFFER;
  snd_pcm_hw_params_set_period_size_near(handle, params, &frames, &dir);

  /* Write the parameters to the driver */
  rc = snd_pcm_hw_params(handle, params);
  if (rc < 0) {
    fprintf(stderr, "unable to set hw parameters: %s\n", snd_strerror(rc));
    return rc;
  }

  /* Use a buffer large enough to hold one period */
  snd_pcm_hw_params_get_period_size(params, &frames, &dir);
  buffersize = frames * 2 * NUM_CHANNELS; /* 2 bytes/sample * channels */
  buffer = (unsigned char*) malloc(buffersize);

  /* We want to loop forever */
  //snd_pcm_hw_params_get_period_time(params, &val, &dir);

  return 0;
}


int arStartRecording(void)
{
    if(running) return 1;

  if(pthread_mutex_init(&mutex, NULL))
  {
    printf("Unable to initialize mutex\n");
    return -1;
  }

  if(pthread_create(&thr, NULL, &entry_point, NULL))
  {
    fprintf(stderr, "Could not create recorder thread!\n");
        running = FALSE;
    return -1;
  }

    running = TRUE;
    return 0;
}


void arStopRecording(void)
{
    running = FALSE;
}


void arFree(void)
{
    running = FALSE;
    sleep(500);
  snd_pcm_drain(handle);
  snd_pcm_close(handle);
  pthread_mutex_destroy(&mutex);
  free(buffer);
}
c++ raspberry-pi floating-point char alsa
1个回答
1
投票

这里的问题不是投射,而是表示问题。

音频通常被表示为一系列的样本。有相当多的方法来表示每个样本:在一个范围内,从 -1.0f+1.0f-32767+32767,或许多其他。

阿尔萨事实上支持 多种格式而你选择了 SND_PCM_FORMAT_S16_LE 那就是 -32767+32767. 你可以把它投给 std::int16_t*假设你的C++环境是Little-Endian(几乎可以肯定)。你不能把它投向 float*,为此你需要问一下。SND_PCM_FORMAT_FLOAT_LE

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