Linker Error in Visual Studio Project

Anurag2904

Hi,

I want to play a video in a project i made. I am using Visual Studio 2015 as my IDE for QT development.

In .h file, I have included :

#include <QtMultimedia\qmediaplayer.h>
#include <QtMultimediaWidgets\qvideowidget.h>
#include <qtimer.h>

Below is my code file:

#include "firstvideo.h"

FirstVideo::FirstVideo(QWidget *parent)
	: QDialog(parent)
{
	ui.setupUi(this);
	player = new QMediaPlayer(this);
	vWidget = new QVideoWidget(this);
	player->setVideoOutput(vWidget);
	QString filename = "./SampleVideo_720x480_1mb.mp4";
	player->setMedia(QUrl::fromLocalFile(filename));
	player->setVolume(100);
	QTimer::singleShot(2000, this, SLOT(playMedia()));
	

}

FirstVideo::~FirstVideo()
{

}
void FirstVideo::playMedia()
{
	vWidget->setFullScreen(true);
	vWidget->show();
	player->play();
}

Below is the error:

Severity	Code	Description	Project	File	Line	Suppression State
Error	LNK2019	unresolved external symbol "__declspec(dllimport) public: __cdecl QVideoWidget::QVideoWidget(class QWidget *)" (__imp_??0QVideoWidget@@QEAA@PEAVQWidget@@@Z) referenced in function "public: __cdecl FirstVideo::FirstVideo(class QWidget *)" (??0FirstVideo@@QEAA@PEAVQWidget@@@Z)	FirstQT	C:\Users\Megis_Student\Documents\Visual Studio 2015\Projects\FirstQT\FirstQT\firstvideo.obj

Can some one guide me on how to resolve this?

Thanks,
Anurag

[Added code tags ~kshegunov]

kshegunov

What Qt version are you using?
With which compiler was it built?
Have you added QT += multimediawidgets to your project file?
Could you show what you havein the Qt project file?

Anurag2904

Thanks for the info. I was able to solve this by adding "Qt5Multimedia.lib" and "Qt5MultimediaWidgets.lib" reference at Properties->Linker->Input->Additional Dependencies.

After this, when I run the program in DEBUG mode, i get fellowing error:
QObject: Cannot create children for a parent that is in a different thread.
(Parent is FirstVideo(0x1ad2f5c7970), parent's thread is QThread(0x1ad2f5270c0), current thread is QThread(0x1ad2f5d36d0)
QWidget: Must construct a QApplication before a QWidget
Unhandled exception at 0x00007FFAFDE8B70E (ucrtbase.dll) in FirstQT.exe: Fatal program exit requested.

Using breakpoint, I found that I get this error at: player = new QMediaPlayer(this);
statement.

But when i run in RELEASE mode, I do not get this error and the video plays. Why does this happen? None of classes inherit thread class.

The flow of program is:
main -> create object of MainWindows -> create a dialog for some Graphics view show -> after showing a graphics, close dialog -> Create object of FirstVideo (as above) -> in constructor of First Video create media player instance and play media. This is a naive project, not well organized, so I fear if i will run into some thread issues? I am creating dialogs from Mainwindow and once work of a dialog is complete, I pop a new dialog to show next graphics/video. Some tips will help.

Also, is .pro file created when creating QT application from visual studio? I cannot find it in my project folder. Can it be generated and if yes, then how?

Thanks,
Anurag

aha_1980

@Anurag2904

Thanks for the info. I was able to solve this by adding "Qt5Multimedia.lib" and "Qt5MultimediaWidgets.lib" reference at Properties->Linker->Input->Additional Dependencies.

Windows programs must use debug DLLs when compiled as debug version. therfore you have to link Qt5Multimediad.lib and Qt5MultimediaWidgetsd.lib in that case.

Anurag2904

Hi,

I added debug dll links but i am still getting the same error in Debug mode. Another problem I am facing is with QMediaPlayer, I am creating an instance of Media player and play video in full screen. This works fine (in release mode). After that I added following connect

connect(fplayer, &QMediaPlayer::stateChanged, this, &FirstQT::play1Done);

That is once the video is fully played, then call play1Done method. After adding this connect the video is played in background and not shown on screen. I just hear the audio in background. After video finishes, play1Done() method is called as expected.

Can anyone help, why is my video not playing in foreground?

Thanks,
Anurag