openAL streaming & interruptions

Question

I made an iphone application which uses OpenAL to play many sounds. These sounds are in mp3, quite heavy (more than 1mn)and I stream them (2 buffers per sound) in order to use less memory. To manage interruptions, I use this code :

In OpenALSupport.c file :

  //used to disable openAL during a call
    void openALInterruptionListener ( void   *inClientData, UInt32 inInterruptionState) 
    {
        if (inInterruptionState == kAudioSessionBeginInterruption) 
        {
            alcMakeContextCurrent (NULL);
        }
    }

    //used to restore openAL after a call
    void restoreOpenAL(void* a_context)
    {
        alcMakeContextCurrent(a_context);
    }

In my SoundManager.m file :

 - (void) restoreOpenAL
    {
        restoreOpenAL(mContext);
    }

    //OPENAL initialization
    - (bool) initOpenAL
    {   
        // Initialization
        mDevice = alcOpenDevice(NULL);
        if (mDevice) {
    ...

            // use the device to make a context
            mContext=alcCreateContext(mDevice,NULL);
            // set my context to the currently active one
            alcMakeContextCurrent(mContext);

            AudioSessionInitialize (NULL, NULL, openALInterruptionListener, mContext);

            NSError *activationError = nil;
            [[AVAudioSession sharedInstance] setActive: YES error: &activationError];

            NSError *setCategoryError = nil;

            [[AVAudioSession sharedInstance] setCategory: AVAudioSessionCategoryAmbient error: &setCategoryError];

            ...
    }

And finally in my AppDelegate :

- (void)applicationDidBecomeActive:(UIApplication *)application
{
    [[CSoundManager getInstance] restoreOpenAL];
    ...
}

With this method the sounds are back after a call , but flows seem to be played randomly. Is there a specific way to manage interruption with streaming sounds ? I don't find any article about that.

Thanks for your help.

score 1 · Accepted Answer · answered Jan 13 '11 at 16:26

Ok, I answer to my own question.

I solved the problem by managing error on my streaming method :

- (void) updateStream
{
ALint processed;    
alGetSourcei(sourceID, AL_BUFFERS_PROCESSED, &processed);

while(processed--)
{
    oldPosition = position;

    NSUInteger buffer;

    alSourceUnqueueBuffers(sourceID, 1, &buffer);

    ////////////////////
    //code freshly added
    ALint err = alGetError();
    if (err != 0) 
    {
        NSLog(@"Error Calling alSourceUnQueueBuffers: %d",err);
        processed++;
        //restore old position for the next buffer
        position = oldPosition;
        usleep(10000);
        continue;
    }
    ////////////////////    

    [self stream:buffer];

    alSourceQueueBuffers(sourceID, 1, &buffer);

    ////////////////////
    //code freshly added
    err = alGetError();
    if (err != 0) 
    {
        NSLog(@"Error Calling alSourceQueueBuffers: %d",err);
        processed++;
        usleep(10000);
        //restore old position for the next buffer 
        position = oldPosition;
    }
    ///////////////////
}

}

The general idea is very helpful, thanks. But isn't the position / oldPosition assignment swapped in one of the cases? — Tomas Andrle, Oct 13 '14 at 10:08
It's old code now and I don't use it anymore. But no I don't swap any assignment. I can send you the whole class if you want. — Klem, Oct 14 '14 at 08:16
ah, I didn't notice the first oldPosition = position assignment at the top. All clear now. Thanks! — Tomas Andrle, Oct 14 '14 at 08:32

openAL streaming & interruptions

1 Answers1