Create QAudioBuffer from wav file

Paul Soulsby

I need create an QAudioBuffer from a wav file. I also need to get the properties of the file, such as bits, sample frequency etc.
This is so I can display the waveform and it's properties. I need access to individual sample values, so am assuming QAudioBuffer is my best approach.
For reference, I'm converting an old VB app, which has the following method to do this:

Set dsBuffer(curWave) = DS.CreateSoundBufferFromFile(CommonDialog1.FileName, dsDesc(curWave))

I then need to play the buffer out of the audio output.
I've found plenty of examples of working with realtime audio streams, but not wav files, so have got a bit stuck and would appreciate any tips!
(This is for Windows and OSX).

SGaist

Hi and welcome to devnet,

Wouldn't QMediaPlayer and the QAudioDecoder be more in line with what you want to do ?

Paul Soulsby

Thanks! I've just had a look at those classes. They seem to be OK for getting the audio properties and playing the file, but I can't see anyway to get to the buffer data. I need that for drawing the waveform and I also need to output the sample values to a text file.
Am I missing something with those classes?

SGaist

Then QAudioProbe might be of interest.

Paul Soulsby

Yeah - I did look into that, but found this thread. It looks like it's not compatible with OSX, so I can't use it as it's essential that the software is OSX compatible.
I feel that one of the audio libraries must have a "create buffer from file" method, much like the VB directX one above. I just can't seem to find it or any similar examples.

Paul Soulsby

I ended up solving this by manually reading the wav file byte by byte and then initialising the QAudioBuffer from a QByteArray, read from the appropriate part of the file. Here's the code. Would be good if there was a method in the QAudioBuffer to read from file automatically.

void MainWindow::readWAV(QString wavFile, int waveNum)
{
    QFile m_WAVFile;
    m_WAVFile.setFileName(wavFile);
    if(m_WAVFile.exists()==false)
    {
        qDebug()<<"File doesn't exist";
        return;
    }
    m_WAVFile.open(QIODevice::ReadWrite);

    char strm[4];
    char s[1];
    QByteArray wav;
    quint32 conv;

    qDebug()<<"\nstart";
    qDebug()<<m_WAVFile.read(4);//RIFF
    // m_WAVHeader.RIFF = m_WAVFile.read(4).data();

    m_WAVFile.read(strm,4);//chunk size
    qDebug()<<qFromLittleEndian<quint32>((uchar*)strm);

    m_WAVFile.read(strm,4);//format
    qDebug()<<strm;

    m_WAVFile.read(strm,4);//subchunk1 id
    qDebug()<<strm;

    m_WAVFile.read(strm,4);//subchunk1 size
    qDebug()<<qFromLittleEndian<quint32>((uchar*)strm);

    m_WAVFile.read(strm,2);//audio format
    qDebug()<<qFromLittleEndian<quint32>((uchar*)strm);

    m_WAVFile.read(strm,2);//NumChannels
    conv = qFromLittleEndian<quint32>((uchar*)strm);
    qDebug()<<conv;
    if(conv!=1)
    {
        QMessageBox::warning(this, "Import wav file", "Wav file must be mono",QMessageBox::Ok,QMessageBox::NoButton);
        return;
    }

    m_WAVFile.read(strm,4);//Sample rate
    conv = qFromLittleEndian<quint32>((uchar*)strm);
    qDebug()<<conv;
    if(conv!=11025)
    {
        QMessageBox::warning(this, "Import wav file", "Use file with 11025Hz sample rate for native sample rate",QMessageBox::Ok,QMessageBox::NoButton);
    }

    m_WAVFile.read(strm,4);//Byte rate
    qDebug()<<qFromLittleEndian<quint32>((uchar*)strm);

    m_WAVFile.read(strm,2);//Block Allign
    qDebug()<<qFromLittleEndian<quint32>((uchar*)strm);

    m_WAVFile.read(strm,2);//BPS
    conv = qFromLittleEndian<quint32>((uchar*)strm);
    qDebug()<<conv;
    if(conv!=8)
    {
        QMessageBox::warning(this, "Import wav file", "Wav file must be unsigned 8 bit",QMessageBox::Ok,QMessageBox::NoButton);
        return;
    }

    m_WAVFile.read(strm,4);//subchunk2 id
    qDebug()<<strm;

    m_WAVFile.read(strm,4);//subchunk2 size
    qDebug()<<qFromLittleEndian<quint32>((uchar*)strm);

    outBuffLen[waveNum] = 0;
    while(!m_WAVFile.atEnd())
    {
        m_WAVFile.read(s,1);
        wav.append(s[0]);
    }
    m_WAVFile.close();
    dsBuffer[waveNum] = QAudioBuffer(wav,fmt);
    outBuffLen[waveNum] = dsBuffer[waveNum].sampleCount();
    qDebug()<<" Processed:";
    qDebug()<<outBuffLen[waveNum];
    wavePath[waveNum] = wavFile;
    QFileInfo fileInfo(wavFile);
    waveName[waveNum] = fileInfo.fileName();
}

SGaist

Thanks for coming back !

I also just re-discovered that the spectrum analyser example provides the WavFile class that you could be interested in also.

Paul Soulsby

Ah, I hadn't spotted this library - this is a slightly nicer way to read the header of a wav file than the way I did it. I may switch to this library at some point.