OpenAL playback captured audio data c++

Question

I am trying to create a voice chat program using OpenAL. The networking side of things seems to be ok but I'll take advice on that =]

The problem I am having at the moment is trying to playback captured audio data from the mic. I followed the code found here to get mic input and echo it to the speakers.

This works OK but I can't seem to playback the fully captured audio after the capturing has finished.

When some sound has been captured I store it on a list like so...

for (int i = 0; i < CAP_SIZE; i++)
{
    playbackBuffer.push_back( buffer[i] );
}

and then after the capturing has finished I have tried (and failed) to use the following code to play that audio back

ALuint  playbackSource;
alGenSources(1, &playbackSource);
errorCode = alGetError();

ALuint tempPlayback;
alBufferData(tempPlayback, AL_FORMAT_MONO16, &playbackBuffer.front(), playbackBuffer.size()*sizeof(ALuint), FREQ);

// Attach the playback buffer to the new playback source
alSourcei(playbackSource, AL_BUFFER, tempPlayback);
alSourcePlay(playbackSource);

ALint sState = 0;
do
{
    alGetSourcei(playbackSource, AL_SOURCE_STATE, &sState);
}
while ((sState == AL_PLAYING));

When debugging I can see that playbackBuffer has a lot of data in it and there is a split second of noise played at this point but nowhere near that which was captured.

EDIT: I have added the line

alGenBuffers(1, &tempPlayback);

after creating the tempPlayback and before the call to alBufferData(...) and this now plays for the correct amount of time but all I hear is a high-pitched noise the whole way through.

keghn keghn · Accepted Answer · 2012-06-06T01:54:23

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).

It worked on mint 13 linux laptop. Mint is like ubuntu 12.04

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

int main(void) 
{ 
const ALCchar *   devices; 
const 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)
while (*ptr)
{ 
   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)
while (*ptr)
{ 
   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); 
}

Compile with this:

g++ p.cpp -lalut -lopenal -o p

OpenAL playback captured audio data c++

3 Answers