CODEWITHSUNDEEP
c++qtaudio
Peter
Peter

Reputation: 326

subclassing QIODevice for QAudioDecoder

Qt 5.7

According to the documentation, QAudioDecoder does not support streaming media. But is accepts either a filename or a QIODevice as source. Came the "bright idea": let's subclass QIODevice to create streaming media support.

But I always get an error:

Unable to start decoding process. Stream contains no data.

I have checked and double checked and debugged. Can't figure out what can be the problem.

I'm only testing it, so the code below is by no means final.

header:

class InputBuffer : public QIODevice
{

public:

    InputBuffer(QString fileName);
    ~InputBuffer();

    qint64 readData(char *data, qint64 maxlen);
    qint64 writeData(const char *data, qint64 len);

    bool   isSequential();
    qint64 bytesAvailable();
    qint64 size();


private:

    char*  bufferRef;
    qint64 length;
    qint64 position;

};

implementation:

#include "inputbuffer.h"

InputBuffer::InputBuffer(QString fileName)
{
    QFileInfo fileInfo(fileName);

    length   = fileInfo.size();
    position = 0;

    bufferRef = (char*)malloc(length);

    QFile file(fileName);
    file.open(QFile::ReadOnly);
    file.read(bufferRef, length);
    file.close();

    emit readyRead();
}


InputBuffer::~InputBuffer()
{
    free(bufferRef);
}


qint64 InputBuffer::readData(char *data, qint64 maxlen)
{
    if (position >= length) {
        return -1;
    }

    qint64 readSize = qMin(maxlen, length - position);

    memcpy(data, bufferRef + position, readSize);
    position += readSize;

    return readSize;
}


qint64 InputBuffer::writeData(const char *data, qint64 len)
{
    return -1;
}


bool InputBuffer::isSequential()
{
    return true;
}


qint64 InputBuffer::bytesAvailable()
{
    return length - position;
}


qint64 InputBuffer::size()
{
    return length;
}

usage:

inputBufferRef = new InputBuffer("/home/pp/Zenék/Test.mp3");
inputBufferRef->open(QIODevice::ReadOnly);

audioDecoderRef = new QAudioDecoder();

audioDecoderRef->setAudioFormat(audioFormat);
audioDecoderRef->setSourceDevice(inputBufferRef);

connect(audioDecoderRef, SIGNAL(bufferReady()),               this, SLOT(decoderBufferReady()));
connect(audioDecoderRef, SIGNAL(finished()),                  this, SLOT(decoderFinished()));
connect(audioDecoderRef, SIGNAL(error(QAudioDecoder::Error)), this, SLOT(decoderError(QAudioDecoder::Error)));

audioDecoderRef->start();

Upvotes: 2

Views: 1604

Answers (1)

jpnurmi
jpnurmi

Reputation: 5836

None of your isSequential(), bytesAvailable(), nor size() methods override the respective method in QIODevice, because the signatures don't match. They are all missing a const qualifier. Using the C++11 override keyword when overriding virtual methods helps.

Upvotes: 5

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