如何使用ALSA在缓冲区中录制声音

Question

我开始学习linux和ALSA，我想知道是否有一种方法可以将我从麦克风a录制的声音直接存储到缓冲区。我在这里阅读了http://www.linuxjournal.com/article/6735?page=0,2如何制作我的录音程序。但是我需要的是稍微复杂一点。我需要录制声音，直到我敲琴键。我需要这个的原因是因为我弄乱了RaspberryPI（上面有debian），看我是否可以将它变成声音监视/检测设备。

我的主要问题是，当我尝试使用它来记录（./Rec> name.raw）时，它什么也不做。它只是输出一个空的.raw文件。

#define ALSA_PCM_NEW_HW_PARAMS_API
#include <termios.h>
#include <alsa/asoundlib.h>

struct termios stdin_orig;  // Structure to save parameters

void term_reset() {
        tcsetattr(STDIN_FILENO,TCSANOW,&stdin_orig);
        tcsetattr(STDIN_FILENO,TCSAFLUSH,&stdin_orig);
}

void term_nonblocking() {
        struct termios newt;
        tcgetattr(STDIN_FILENO, &stdin_orig);
        fcntl(STDIN_FILENO, F_SETFL, O_NONBLOCK); // non-blocking
        newt = stdin_orig;
        newt.c_lflag &= ~(ICANON | ECHO);
        tcsetattr(STDIN_FILENO, TCSANOW, &newt);

        atexit(term_reset);
}

int main() {
  int key=0;
  long loops;
  int rc;
  int size;
  snd_pcm_t *handle;
  snd_pcm_hw_params_t *params;
  unsigned int val;
  int dir;
  snd_pcm_uframes_t frames;
  char *buffer;

  /* Open PCM device for recording (capture). */
  rc = snd_pcm_open(&handle, "default", SND_PCM_STREAM_CAPTURE, 0);
  if (rc < 0) {
    fprintf(stderr, "unable to open pcm device: %s\n", snd_strerror(rc));
    exit(1);
  }

  /* 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);

  /* One channel (mono) */
  snd_pcm_hw_params_set_channels(handle, params, 1);

  /* 16000 bits/second sampling rate */
  val = 16000;
  snd_pcm_hw_params_set_rate_near(handle, params, &val, &dir);

  /* Set period size to 2048 frames. */
  frames = 2048;
  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));
    exit(1);
  }

  /* Use a buffer large enough to hold one period */
  snd_pcm_hw_params_get_period_size(params, &frames, &dir);
  size = frames * 2; /* 2 bytes/sample, 1 channels */
  buffer = (char *) malloc(size);

  while (key == 0) 
  {

    rc = snd_pcm_readi(handle, buffer, frames);
    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));
    } 
    else if (rc != (int)frames) 
    {
      fprintf(stderr, "short read, read %d frames\n", rc);
    }

    rc = write(1, buffer, size);

    if (rc != size)
      fprintf(stderr, "short write: wrote %d bytes\n", rc);
    key = getchar();
  }

  snd_pcm_drain(handle);
  snd_pcm_close(handle);
  free(buffer);

  return 0;
}

Answer 1

这是我使用python做到的方式。经过测试，可以在带USB Plantronics耳机的台式机Debian上使用。您需要安装python-qt4和python-pyaudio软件包才能运行。

此外，您需要将输入设备设置为麦克风。在GNOME中，我通过System Tools -> System Settings-> Sound切换了输入和输出设备。如果您像我一样在Raspberry上有Raspbian而不是Debian，它将变得更加困难，因为这里有LXDE而不是GNOME。您可以使用alsamixer和F6按钮在那里设置声卡，但是问题是ALSA是低级接口，而most Linuxes use some sound server on top of it是PulseAudio或JACK。您需要一些运气/时间，以确保将输入/输出设备切换到麦克风/耳机。

[如果您使用通过Raspberry Pi的Jack输入插入的Jack麦克风，请注意，Raspberry的Jack仅是输入，因此您将无法播放录音，而需要一些USB耳机来收听您的wav。 >

就我个人而言，我认为ALSA的文献记录很少（我想是故意的job security），我不喜欢处理它。

import pyaudio
import wave
import sys
from PyQt4.QtCore import *
from PyQt4.QtGui import *

# This is Qt part: we create a window, which has a "stop" flag.
# Stop flag defaults to False, but is set to True, when you press a key.
# Value of that flag is checked in main loop and loop exits when flag is True.

app = QApplication(sys.argv)
class MyWindow(QWidget):
    def __init__(self):
        super(QWidget, self).__init__()
        self.stop = False
    def keyPressEvent(self, event):
        print "keyPressedEvent caught!"
        self.stop = True

window = MyWindow()
window.show()

# This is sound processing part: we create an input stream to read from microphone.

p = pyaudio.PyAudio()
stream = p.open(format = p.get_format_from_width(2),
        channels = 2,
        rate=44100,
        input=True,
        output=False,
        frames_per_buffer=1024)

# This is main loop: we iteratively poll audio and gui: audio data are stored in output_buffer,
# whereas gui is checked for stop flag value (if keyPressedEvent happened, flag will be set
# to True and break our main loop).

output_buffer = ""
while True:
    app.processEvents()
    data = stream.read(1024)
    output_buffer += data
    if window.stop: break

stream.stop_stream()
stream.close()

# Here we output contents of output_buffer as .wav file
output_wav = wave.open("output.wav", 'w')
output_wav.setparams((2, 2, 44100, len(output_buffer),"NONE","not compressed"))
output_wav.writeframesraw(output_buffer)

p.terminate()

Answer 2

此代码显示了如何在while循环中从C ++中的ALSA捕获：https://github.com/flatmax/gtkiostream/blob/master/test/ALSACaptureTest.C#L95