Downloading a video from youtube

[Faster]

Hi, what qt4 class could I use to download a video from youtube? I need to download a video from an url like this: http://youtube.com/get_video?video_i...xA5rvs=&fmt=18. Firefox download this video but Qhttp fails to download. Any suggestions?
This is my code:

QString video_url = "http://youtube.com/get_video";
    QString argument = "?video_id=Th7-EzW0Ccw&t=vjVQa1PpcFNQDXk1DXroxSYaUxdfZ23C8lngRxA5rvs=&fmt=18";
    QString dest = "/home/faster/video.mp4";
 
    QUrl url(video_url);
    QFileInfo fileInfo(url.path());
    QString fileName = fileInfo.fileName();
    if (fileName.isEmpty())
        fileName = "index.html";
 
    file = new QFile(dest);
 
    QHttp::ConnectionMode mode = url.scheme().toLower() == "https" ? QHttp::ConnectionModeHttps : QHttp::ConnectionModeHttp;
    http->setHost(url.host(), mode, url.port() != -1 ? url.port() : 80);
 
    if (!url.userName().isEmpty())
        http->setUser(url.userName(), url.password());
 
    httpRequestAborted = false;
    QByteArray path = QUrl::toPercentEncoding(url.path(), "!$&'()*+,;=:@/");
    if (path.isEmpty())
        path = "/";
    httpGetId = http->get(video_url+argument, file);

QString video_url = "http://youtube.com/get_video";
    QString argument = "?video_id=Th7-EzW0Ccw&t=vjVQa1PpcFNQDXk1DXroxSYaUxdfZ23C8lngRxA5rvs=&fmt=18";
    QString dest = "/home/faster/video.mp4";
    
    QUrl url(video_url);
    QFileInfo fileInfo(url.path());
    QString fileName = fileInfo.fileName();
    if (fileName.isEmpty())
        fileName = "index.html";

    file = new QFile(dest);

    QHttp::ConnectionMode mode = url.scheme().toLower() == "https" ? QHttp::ConnectionModeHttps : QHttp::ConnectionModeHttp;
    http->setHost(url.host(), mode, url.port() != -1 ? url.port() : 80);

    if (!url.userName().isEmpty())
        http->setUser(url.userName(), url.password());

    httpRequestAborted = false;
    QByteArray path = QUrl::toPercentEncoding(url.path(), "!$&'()*+,;=:@/");
    if (path.isEmpty())
        path = "/";
    httpGetId = http->get(video_url+argument, file);

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