QGraphicsVideoItem crashes on video play

[tuli]

Hi!

I am trying to implement a zoom-able video playing, which is only possible by using QGraphicsVideoItem in a QGraphicssView, I have been told. This would be a basic example:

QGraphicsView * graphicsView = new QGraphicsView;
		QMediaPlayer * player = new QMediaPlayer;
 
		QGraphicsScene * scene = new QGraphicsScene;
		graphicsView->setScene(scene);
 
		QGraphicsVideoItem *item = new QGraphicsVideoItem;
		player->setVideoOutput(item);
		graphicsView->scene()->addItem(item);
		graphicsView->show();
 
		player->setMedia(QUrl::fromLocalFile("c:/x.mp4"));
		player->play();

QGraphicsView * graphicsView = new QGraphicsView;
		QMediaPlayer * player = new QMediaPlayer;

		QGraphicsScene * scene = new QGraphicsScene;
		graphicsView->setScene(scene);

		QGraphicsVideoItem *item = new QGraphicsVideoItem;
		player->setVideoOutput(item);
		graphicsView->scene()->addItem(item);
		graphicsView->show();

		player->setMedia(QUrl::fromLocalFile("c:/x.mp4"));
		player->play();

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however, it chokes on a debug assert:

---------------------------
Microsoft Visual C++ Runtime Library
---------------------------
Debug Error!

Program: C:\Qt5\5.4\msvc2013_64\bin\Qt5Cored.dll
Module: 5.4.1
File: global\qglobal.cpp
Line: 2868

ASSERT: "m_surface" in file player\mfvideorenderercontrol.cpp, line 2342

(Press Retry to debug the application)

---------------------------
Abort Retry Ignore
---------------------------

I looked into it, but I have no idea why the assert is fired.

Q_ASSERT(m_surface);

As far as i can tell, m_surface is non-NULL.



Anyways, the crash also occurs when I just create a QGraphicsVideoItem without adding it to anything.

QMediaPlayer * player = new QMediaPlayer;
		QGraphicsVideoItem *item = new QGraphicsVideoItem;
		player->setVideoOutput(item);
 
		player->setMedia(QUrl::fromLocalFile("c:/x.mp4"));
		player->play();

QMediaPlayer * player = new QMediaPlayer;
		QGraphicsVideoItem *item = new QGraphicsVideoItem;
		player->setVideoOutput(item);

		player->setMedia(QUrl::fromLocalFile("c:/x.mp4"));
		player->play();

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i can only guess that the crash is related to the QGraphicsVideoItem not offering a proper surface to render the video on? Where do I go wrong?


I am using Qt 5.4 + MSVC 2013 + Win7.

[wysota]

Do you have proper video backend for your platform installed?

[tuli]

Yes. I can play the video fine with a QVideoWidget.

[wysota]

Did you add the item to a scene? Aah, I see you did. Can you prepare a minimal compilable example reproducing the problem?

[tuli]

Sure!

Just adjust the path to the mp4 file.

#include <QWidget>
#include <QtCore>
#include <QtGui>
#include <QtWidgets>
#include <QtMultimedia>
 
#include <QGraphicsVideoItem>
 
int main(int argc, char *argv[])
{
	QApplication a(argc, argv);
 
	QMediaPlayer * player = new QMediaPlayer;
	QGraphicsVideoItem *item = new QGraphicsVideoItem;
	player->setVideoOutput(item);
	player->setMedia(QUrl::fromLocalFile("c:/x.mp4"));
	player->play();
 
	return a.exec();
}

#include <QWidget>
#include <QtCore>
#include <QtGui>
#include <QtWidgets>
#include <QtMultimedia>

#include <QGraphicsVideoItem>

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

	QMediaPlayer * player = new QMediaPlayer;
	QGraphicsVideoItem *item = new QGraphicsVideoItem;
	player->setVideoOutput(item);
	player->setMedia(QUrl::fromLocalFile("c:/x.mp4"));
	player->play();

	return a.exec();
}

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[wysota]

Well, here you are not adding the item to a scene.

This works for me:

#include <QApplication>
#include <QMediaPlayer>
#include <QGraphicsVideoItem>
#include <QGraphicsView>
#include <QGraphicsScene>
 
int main(int argc, char *argv[])
{
        QApplication a(argc, argv);
        QMediaPlayer * player = new QMediaPlayer;
        QGraphicsVideoItem *item = new QGraphicsVideoItem;
        player->setVideoOutput(item);
        player->setMedia(QUrl::fromLocalFile("/tmp/a/sintel_trailer-480p.mp4"));
        QGraphicsScene scene;
        scene.addItem(item);
        QGraphicsView view;
        view.setScene(&scene);
        view.show();
        player->play();
        return a.exec();
}

#include <QApplication>
#include <QMediaPlayer>
#include <QGraphicsVideoItem>
#include <QGraphicsView>
#include <QGraphicsScene>

int main(int argc, char *argv[])
{
        QApplication a(argc, argv);
        QMediaPlayer * player = new QMediaPlayer;
        QGraphicsVideoItem *item = new QGraphicsVideoItem;
        player->setVideoOutput(item);
        player->setMedia(QUrl::fromLocalFile("/tmp/a/sintel_trailer-480p.mp4"));
        QGraphicsScene scene;
        scene.addItem(item);
        QGraphicsView view;
        view.setScene(&scene);
        view.show();
        player->play();
        return a.exec();
}

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[tuli]

Both your and my snippet cause the described crash.