How can I use Qt to encrypt/decrypte/play a video? - qt

Question

I am looking for a way to encrypt an video file and then use decrypt it to ram and play it directly.

Answer 1

setMedia takes a QIOdevice as second argument:
#include <QMediaPlayer>
#include <QApplication>
#include <QFile>
int main(int argc, char ** argv)
{
QApplication app(argc,argv);
QString fileName = app.arguments().at(1);
QFile io(fileName);
io.open(QFile::ReadOnly);
QMediaPlayer player;
player.setMedia(QUrl("test.mp3"), &io);
player.play();
return app.exec();
}
but just in case you really mean QDataStream:
QDataStream is buffered io, QIODevice is direct io, they're not compatible, so you have to double buffer like this:
#include <QMediaPlayer>
#include <QApplication>
#include <QFile>
#include <QBuffer>
#include <QDataStream>
int main(int argc, char ** argv)
{
QApplication app(argc,argv);
QString fileName = app.arguments().at(1);
// our double buffer
QByteArray bufferSpace;
// our stream on which we can put "media" data
QDataStream stream(&bufferSpace, QIODevice::WriteOnly);
// this is just demo data
QFile io(fileName);
io.open(QFile::ReadOnly);
stream << io.readAll();
// open an IO Device on our buffer
QBuffer buffer(&bufferSpace);
buffer.open(QBuffer::ReadOnly);
// give the IO to the media player
QMediaPlayer player;
player.setMedia(QUrl("test.mp3"), &buffer);
player.play();
return app.exec();
}
edit
here's a faster version of that "crypto" code you posted without using a buffer for the entire file:
#include <QMediaPlayer>
#include <QApplication>
#include <QFile>
#include <QBuffer>
#include <QDataStream>
static const unsigned char key = 0xAB;
class MyFunnyCrypto : public QFile /*or subclass any other IO*/
{
protected:
virtual qint64 readData(char *data, qint64 maxSize)
{
qint64 r = QFile::readData(data, maxSize);
if (r > 0) {
for (qint64 i = 0; i < r; i++) {
data[i] = data[i]^key;
}
}
return r;
}
};
int main(int argc, char ** argv)
{
QApplication app(argc,argv);
QString fileName = app.arguments().at(1);
MyFunnyCrypto io;
io.setFileName(fileName);
io.open(QFile::ReadOnly);
// give the IO to the media player
QMediaPlayer player;
player.setMedia(QUrl("test.mp3"), &io);
player.play();
return app.exec();
}

Answer 2

Thanks to #aep .
It doesn't have anything to do with QDataStream, and it's quite simple.
Encryption:
unsigned char key = 0xAB;
QFile file("test.mp3");
file.open(QIODevice::ReadOnly);
QByteArray byteArray = file.readAll();
for(int i=1024;i<byteArray.length();i++){
byteArray[i] = byteArray[i]^key;
}
file.close();
QFile encrypted("encrypted.mp3");
encrypted.open(QIODevice::WriteOnly);
encrypted.write(byteArray);
encrypted.close();
And decryption:
unsigned char key = 0xAB;
QFile file("encrypted.mp3");
file.open(QIODevice::ReadOnly);
auto byteArray = file.readAll();
for(int i=1024;i<byteArray.length();i++){
byteArray[i] = byteArray[i]^key;
}
QBuffer buffer(&byteArray);
buffer.open(QBuffer::ReadOnly);
// give the IO to the media player
QMediaPlayer player;
player.setMedia(QUrl(), &buffer);
player.play();
In the for-loop, I want to declare i as qint64 rather than int. But the compiler shows QByteArray::​operator[](int i).