How to use QtConcurrent to qCompress on QByteArray?

I want to write a little program which compress all files from a directory by using qCompress of QByteArray.

However i want to run the compression on a multithreaded environment by using QtConcurrent. But i have some problems.

Here my code :

FilePool pool(folder,suffix);
QFutureWatcher<QString> watcher;
QProgressDialog progressDialog;


connect(&watcher,SIGNAL(progressRangeChanged(int,int)),&progressDialog,SLOT(setRange(int,int)));

connect(&watcher,SIGNAL(progressValueChanged(int)),&progressDialog,SLOT(setValue(int)));

connect(&progressDialog,SIGNAL(canceled()),&watcher,SLOT(cancel()));

QFuture<QString> future = QtConcurrent::filtered(pool,FindInFile(search));
QString text;

watcher.setFuture(future);

progressDialog.exec();

future.waitForFinished();
//Test for compressing file

QFile outFile("testCompress.ecf");
outFile.open(QIODevice::WriteOnly);
QByteArray nonCompressedData;
foreach(const QString &file,future.results()){
    //Fichier d'entrée
    QFile inFile(file);
    inFile.open(QIODevice::ReadOnly);
    nonCompressedData.append(inFile.readAll());
    inFile.close();
    text += file + "\n";
}

//QByteArray compressedData(qCompress(nonCompressedData,9));
//PROBLEM HERE
QFuture<QByteArray> futureCompressor = QtConcurrent::filtered(nonCompressedData,qCompress);
futureCompressor.waitForFinished();
QByteArray compressedData = futureCompressor.results();

outFile.write(compressedData);

The problem is that the compiler raise me an errors

First : No matching function for call to filtered(&QByteArray,).

Second : converstion from QList to non scalar type QByteArray requested.

So, my question is,is it possible to do what i want?

Thanks in advance