QVector<QVector<int>> buffer(16) // 4 * 4 : numberOfChannels * numberOfFiles
for(int i = 0 ; i < 4 ; i++){ 
	QFile file(fileList[i]);	// fileList is QList of QStrings contains 4 files path
	if(file.open(QIODevice::ReadOnly)){
		int k = 0;
		while(!file.atEnd()){
			QByteArray sample = file.read(depth/8); // depth here is 24
			int integerSample = convertByteArrayToIntFunction(sample);
			buffer[4 * i + (K%4)].append(integerSample);	
			k++;

		}
	}
}

To have at the end this matrix of 16 columns like below(f:file, c:channel):
f1c0 | f1c1 | f1c2 | f1c3 | f2c0 | f2c1 | ... | f4c2 | f4c3

But this approach it takes ages for large files of few gigabytes. I am wondering if there is another efficient way to fulfill this task and gain a lot of time.
Thanks in advance.