Re: playback captured audio from mic

Jason Daly <[email protected]> Mon, 30 Aug 2010 13:48:19 -0400

Newsgroups	gmane.comp.lib.openal
Message-ID	<[email protected]>

[email protected] wrote:
> Hi all,
>
> I'm fighting for a week now with openal to be able to do this exact 
> thing "Capture (from mic) and playback the recorded audio" or at least 
> "Capture (from mic) and save the audio to a .wav file". I read a bunch 
> of post on different forums about it, but non of them shows a complete 
> working example, the just say "try to fix this or that" or "you miss to 
> do that..", so, it becoming a nightmare to try to mix different answers 
> to diferent potential problems in the code...
>
> So, anyone have a fully working simple sample about how to do that?, 
> hopefully a linux one...
>   

Mauricio,

Here's a really simple program that captures audio for 5 seconds, 
pauses, then captures 5 more seconds of audio, and finally plays it all 
back (I used it to debug a problem with capture one time).

Maybe it'll be useful for you...

--"J"

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testcapture.c (text/x-csrc, 5.6 KB)

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <AL/al.h>
#include <AL/alc.h>
#include <sys/time.h>

int main(void)
{
   const ALCchar *   devices;
   ALCchar *         ptr;
   ALCdevice *       mainDev;
   ALCcontext *      mainContext;
   ALCdevice *       captureDev;
   ALubyte           captureBuffer[1048576];
   ALubyte           *captureBufPtr;
   ALint             samplesAvailable;
   ALint             samplesCaptured;
   time_t            currentTime;
   time_t            lastTime;
   ALuint            buffer;
   ALuint            source;
   ALint             playState;
   int               i;

   // Print the list of capture devices
   printf("Available playback devices:\n");
   devices = alcGetString(NULL, ALC_DEVICE_SPECIFIER);
   ptr = devices;
   while (ptr[0] != NULL)
   {
       printf("   %s\n", ptr);
       ptr += strlen(ptr) + 1;
   }

   // Open a playback device and create a context first
   printf("Opening playback device:\n");
   mainDev = alcOpenDevice(NULL);
   if (mainDev == NULL)
   {
      printf("Unable to open playback device!\n");
      exit(1);
   }
   devices = alcGetString(mainDev, ALC_DEVICE_SPECIFIER);
   printf("   opened device '%s'\n", devices);
   mainContext = alcCreateContext(mainDev, NULL);
   if (mainContext == NULL)
   {
      printf("Unable to create playback context!\n");
      exit(1);
   }
   printf("   created playback context\n");

   // Make the playback context current
   alcMakeContextCurrent(mainContext);
   alcProcessContext(mainContext);

   // Print the list of capture devices
   printf("Available capture devices:\n");
   devices = alcGetString(NULL, ALC_CAPTURE_DEVICE_SPECIFIER);
   ptr = devices;
   while (ptr[0] != NULL)
   {
       printf("   %s\n", ptr);
       ptr += strlen(ptr) + 1;
   }

   // Open the default device
   printf("Opening capture device:\n");
   captureDev = alcCaptureOpenDevice(NULL, 8000, AL_FORMAT_MONO16, 800);
   if (captureDev == NULL)
   {
      printf("   Unable to open device!\n");
      exit(1);
   }
   devices = alcGetString(captureDev, ALC_CAPTURE_DEVICE_SPECIFIER);
   printf("   opened device %s\n", devices);

   // Wait for three seconds to prompt the user
   for (i = 3; i > 0; i--)
   {
      printf("Starting capture in %d...\r", i);
      fflush(stdout);
      lastTime = time(NULL);
      currentTime = lastTime;
      while (currentTime == lastTime)
      {
         currentTime = time(NULL);
         usleep(100000);
      }
   }

   printf("Starting capture NOW!\n");
   fflush(stdout);
   lastTime = currentTime;

   // Capture (roughly) five seconds of audio
   alcCaptureStart(captureDev);
   samplesCaptured = 0;
   captureBufPtr = captureBuffer;
   while (currentTime < (lastTime + 5))
   {
      // Get the number of samples available
      alcGetIntegerv(captureDev, ALC_CAPTURE_SAMPLES, 1, &samplesAvailable);

      // Copy the samples to our capture buffer
      if (samplesAvailable > 0)
      {
         alcCaptureSamples(captureDev, captureBufPtr, samplesAvailable);
         samplesCaptured += samplesAvailable;
         printf("Captured %d samples (adding %d)\r", samplesCaptured,
            samplesAvailable);
         fflush(stdout);

         // Advance the buffer (two bytes per sample * number of samples)
         captureBufPtr += samplesAvailable * 2;
      }

      // Wait for a bit
      usleep(10000);

      // Update the clock
      currentTime = time(NULL);
   }
   printf("\nPausing capture.\n");
   alcCaptureStop(captureDev);

   // Wait for three seconds to prompt the user
   for (i = 3; i > 0; i--)
   {
      printf("Resuming capture in %d...\r", i);
      fflush(stdout);
      lastTime = time(NULL);
      currentTime = lastTime;
      while (currentTime == lastTime)
      {
         currentTime = time(NULL);
         usleep(100000);
      }
   }

   printf("Resuming capture NOW!\n");
   fflush(stdout);
   lastTime = currentTime;

   // Capture (roughly) five seconds of audio
   alcCaptureStart(captureDev);
   while (currentTime < (lastTime + 5))
   {
      // Get the number of samples available
      alcGetIntegerv(captureDev, ALC_CAPTURE_SAMPLES, 1, &samplesAvailable);

      // Copy the samples to our capture buffer
      if (samplesAvailable > 0)
      {
         alcCaptureSamples(captureDev, captureBufPtr, samplesAvailable);
         samplesCaptured += samplesAvailable;
         printf("Captured %d samples (adding %d)\r", samplesCaptured,
            samplesAvailable);
         fflush(stdout);

         // Advance the buffer (two bytes per sample * number of samples)
         captureBufPtr += samplesAvailable * 2;
      }

      // Wait for a bit
      usleep(10000);

      // Update the clock
      currentTime = time(NULL);
   }

   printf("\nDone capturing.\n");
   alcCaptureStop(captureDev);

   // Play back the captured data
   printf("Starting playback...\n");
   fflush(stdout);
  
   // Generate an OpenAL buffer for the captured data
   alGenBuffers(1, &buffer);
   alGenSources(1, &source);
   alBufferData(buffer, AL_FORMAT_MONO16, captureBuffer,
      samplesCaptured*2, 8000);
   alSourcei(source, AL_BUFFER, buffer);
   alSourcePlay(source);

   // Wait for the source to stop playing
   playState = AL_PLAYING;
   while (playState == AL_PLAYING)
   {
      printf("  source %d is playing...\r", source);
      fflush(stdout);
      alGetSourcei(source, AL_SOURCE_STATE, &playState);
      usleep(100000);
   }
   printf("\nDone with playback.\n");
   fflush(stdout);

   // Shut down OpenAL
   alDeleteSources(1, &source);
   alDeleteBuffers(1, &buffer);
   alcMakeContextCurrent(NULL);
   alcCloseDevice(mainDev);
   alcCaptureCloseDevice(captureDev);
}