Assertion 's' failed at pulse/stream.c while restarting QAudioOutput and QAudioInput?

[the_naive]

My application uses QAudioOutput and QAudioInput for audio communication between different audio devices. So, a user can speak through a microphone and that can be heard through a speaker using this app. It has a push-to-talk feature where the user can push a button on the app or a key on the keyboard to activate speaking through a microphone for the very moment when the button or the key is pressed.

The problem is that when push-to-talk option is used in quick succession, like when the user presses and releases the button in very quick succession for several times, like 5-6 times, sometimes the application crashes with an error message that says:

Assertion 's' failed at pulse/stream.c:1662, function pa_stream_writable_size(). Aborting.
Aborted

My OS is Ubuntu 14.04 LTS.

The methods for starting and stopping the microphone and the speaker are as below:

void AudioSettings::pushToTalk_pressed()
{
    if(output->state() != QAudio::ActiveState && input->state() != QAudio::ActiveState)
    {
        output->start(input->start());
    }
}
 
void AudioSettings::pushToTalk_released()
{   
    if(output->state() == QAudio::ActiveState && input->state() == QAudio::ActiveState)
    {
        output->stop();
        input->stop();
     }
}

void AudioSettings::pushToTalk_pressed()
{
    if(output->state() != QAudio::ActiveState && input->state() != QAudio::ActiveState)
    {
        output->start(input->start());
    }
}

void AudioSettings::pushToTalk_released()
{   
    if(output->state() == QAudio::ActiveState && input->state() == QAudio::ActiveState)
    {
        output->stop();
        input->stop();
     }
}

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Here input and output are respectively pointers to object of QAudioInput and QAudioOutput. They are initialized in the following way:

QAudioFormat audioFormat;
audioFormat.setChannelCount(2);
audioFormat.setCodec("audio/pcm");
audioFormat.setSampleRate(22050);
audioFormat.setSampleSize(16);
audioFormat.setByteOrder(QAudioFormat::LittleEndian);
audioFormat.setSampleType(QAudioFormat::SignedInt);
 
QAudioDeviceInfo outputDevinfo = ui->output2Box->itemData(ui->output2Box->currentIndex()).value<QAudioDeviceInfo>();
 
if (!outputDevinfo.isFormatSupported(audioFormat))
{
   //Default format not supported - trying to use nearest
   audioFormat = outputDevinfo.nearestFormat(audioFormat);
}
 
//Initializing output device        
output = new QAudioOutput(outputDevinfo, audioFormat, this);
 
QAudioDeviceInfo inputDevinfo = ui->input2Box->itemData(ui->input2Box->currentIndex()).value<QAudioDeviceInfo>();
 
 
if (!inputDevinfo.isFormatSupported(audioFormat))
{
   //Default format not supported - trying to use nearest
   audioFormat = inputDevinfo.nearestFormat(audioFormat);
}
 
//Initializing input device
input = new QAudioInput(inputDevinfo, audioFormat, this);

QAudioFormat audioFormat;
audioFormat.setChannelCount(2);
audioFormat.setCodec("audio/pcm");
audioFormat.setSampleRate(22050);
audioFormat.setSampleSize(16);
audioFormat.setByteOrder(QAudioFormat::LittleEndian);
audioFormat.setSampleType(QAudioFormat::SignedInt);

QAudioDeviceInfo outputDevinfo = ui->output2Box->itemData(ui->output2Box->currentIndex()).value<QAudioDeviceInfo>();

if (!outputDevinfo.isFormatSupported(audioFormat))
{
   //Default format not supported - trying to use nearest
   audioFormat = outputDevinfo.nearestFormat(audioFormat);
}

//Initializing output device        
output = new QAudioOutput(outputDevinfo, audioFormat, this);

QAudioDeviceInfo inputDevinfo = ui->input2Box->itemData(ui->input2Box->currentIndex()).value<QAudioDeviceInfo>();


if (!inputDevinfo.isFormatSupported(audioFormat))
{
   //Default format not supported - trying to use nearest
   audioFormat = inputDevinfo.nearestFormat(audioFormat);
}

//Initializing input device
input = new QAudioInput(inputDevinfo, audioFormat, this);

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I tried to use GDB for finding out why this crash happens, but I only get the result in call stack of QtCreator as shown in the image.
Screenshot from 2016-05-11 15:27:22.jpg
Could anyone please tell me how to prevent the aforementioned crash?

Thanks.