Terrible performance with QMediaPlayer and QVideoWidget

Question

I see a terrible performance while trying to play videos with QtMobility 1.2.0 and Qt 4.7.4 on Ubuntu 10.10 (Pentium 4 2.80GHz).

What's funny is that totem (which also use gstreamer as backend) and vlc are able to play these videos without a problem on this machine, even with higher resolutions (fullscreen, etc).

According to top, my application consumes 100% of CPU while totem and vlc consumes only ~ 40%. That's... weird! So I'm sharing the source code of the application below. It uses QMediaPlayer and QVideoWidget to do the job.

movie.cpp:

#include <QtGui/QMainWindow>
#include <QtGui>
#include <qmediaplayer.h>
#include <qvideowidget.h>

int main(int argc, char* argv[])
{
    QApplication app(argc, argv);

    QMainWindow mainWindow;

    mainWindow.resize(QSize(1280, 500));

    QMediaPlayer* mplayer = new QMediaPlayer;
    QVideoWidget* vid_widget = new QVideoWidget(&mainWindow);
    vid_widget->setAspectRatioMode(Qt::IgnoreAspectRatio);

    mainWindow.setCentralWidget(vid_widget);

    mplayer->setVideoOutput(vid_widget);
    mplayer->setMedia(QUrl::fromLocalFile(argv[1]));
    mplayer->setVolume(50);
    mplayer->setPlaybackRate(1);
    mplayer->play();

    mainWindow.show();

    return app.exec();
}

movie.pro:

TEMPLATE = app
QT += gui 

CONFIG += mobility
MOBILITY = multimedia

QMAKE_RPATHDIR += $$DESTDIR

SOURCES = \
movie.cpp

The performance remains awful even if I create a smaller window, such as:

mainWindow.resize(QSize(960, 540));

Does anyone know what could be causing this behavior and how do I fix it?

If anyone is interested, ffmpeg shows this information about one of the video files I'm using for testing:

Input #0, matroska, from '/home/user/movie.mkv':
  Duration: 00:02:23.22, start: 0.000000, bitrate: N/A
    Stream #0.0(eng): Video: h264, yuvj420p, 1280x536 [PAR 1:1 DAR 160:67], 23.98 fps, 23.98 tbr, 1k tbn, 47.95 tbc
    Stream #0.1(eng): Audio: aac, 48000 Hz, stereo, s16

Answer 1

There is nothing wrong with your code, you are just passing the ball to Qt for the decoding and playback of the movie.

You are either using a build of Qt that doesn't have hardware acceleration enabled, or your system doesn't have the proper hardware for Qt to accelerate decoding and playback.

Answer 2

I started using QML Video Element and after having several rendering/performance problems with it I finally gave up and wrote a video player element to replace the one from QtMobility.

To whoever might be interested, GStreamer has a C++ interface that is very easy to use.