Problem with Qt Multimedia

6EQUJ5

I have a very strange issue with QMediaPlayer. I created a new Qt Widgets Application project. In the MainWindow class (in mainwindow.h) I wrote this: QMediaPlayer *player = new QMediaPlayer(this);

In mainwindow.h I also wrote #include <QMultimedia/QMediaPlayer>
Since building gave me an undefined reference error to QMediaPlayer, in project-name.pro I added QT += multimedia

Then building my project went smoothly. This is the really strange part: when I ran the executable generated, it logged me out of my laptop! As in I had to log into my laptop again!

Any idea why this happens? How to fix?

P.S. I am using Qt 5.8.0 on Debian 8

KhoaTran Programmer

Hi 6EQUJ5,

Could you please show up more detail about your error?

I've had times for working with Qt Multimedia for Embedded Linux, my experience is that Qt uses Gstreamer framework as the backend layer for Multimedia function. So maybe you must install Gstreamer on your Linux firstly.

Best regards,
Khoa

6EQUJ5

@KhoaTran-Programmer The errors are here:

path/mainwindow.o In function `MainWindow::MainWindow(QWidget*)':

path/mainwindow.cpp:-1: error: undefined reference to `QMediaPlayer::QMediaPlayer(QObject*, QFlagsQMediaPlayer::Flag)'

:-1: error: collect2: error: ld returned 1 exit status

Adding QT += multimedia in project_name.pro solved it. But, as I stated it logs me off for some reason when I run it.

SGaist

Hi and welcome to devnet,

You are missing QT += multimediawidgets in your .pro file.

6EQUJ5

@SGaist The same problem happens. I tried adding just QT += multimedia, just QT += multimediawidgets, and both of them in my .pro file.

SGaist

Did you re-run qmake after modifying the QT variable ?

6EQUJ5

@SGaist Yes I did. I cleaned, ran qmake, then rebuilded.

SGaist

Ok, can you show how you create your QMediaPlayer object ?

Re-reading the error message, it seems that you are trying to give it a QObject based parent rather than a QWidget based parent.

6EQUJ5

@SGaist I created my QMediaPlayer object like this:

___QMediaPlayer *player = new QMediaPlayer(this);

SGaist

What is this ?

6EQUJ5

@SGaist this is MainWindow.

mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <QtMultimedia/QMediaPlayer>

namespace Ui
{
    class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();

private:
    QMediaPlayer *player = new QMediaPlayer(this);
    Ui::MainWindow *ui;
};

#endif // MAINWINDOW_H

KhoaTran Programmer

@6EQUJ5 ,

Could you please try to run some media player that has already had in Qt package

Qt5.8.0\Examples\Qt-5.8\multimedia\video\qmlvideo
Qt5.8.0\Examples\Qt-5.8\multimediawidgets\player

You should ensure that the Multimedia backend is available on your system or not?

Best regards,
Khoa

6EQUJ5

@KhoaTran-Programmer With qmlvideo when I tried to play a video it logged me out again. With player it logged me out the moment I ran it.

Why do I get logged out when I try to run multimedia based Qt programs? And how do I ensure the multimedia back end is available on my system and install the multimedia backend?

SGaist

You should start by testing with your distribution provided Qt to ensure that everything is working correctly.

KhoaTran Programmer

@6EQUJ5

How to ensure the multimedia backend is available or not? I try 2 methods before:

Use default application of Qt(qmlvideo, player, ...)
-> If one of them can run well, we can conclude it's OK
Download Qt everywhere package and install(I try on Linux Embedded)
-> When building Qt Multimedia component, qmake will automatically detect the backend, if it's not available some error info will display

For your information, multimedia backend is not same for each OS

Windows: Directshow -> it's always available in Windows
Linux: Gstreamer -> Most, if not all, Linux distributions provide packages of GStreamer. You should find these in your distribution's package repository.
QNX: ???
Android: StageFight(maybe)

Since your OS is Linux(Debian 8), so please confirm Gstreamer firstly. The fastest way, open termial and run some Gstreamer command line tools:
$ gst-inspect-1.0
$ gst-launch-1.0

For set up Gstreamer on Linux, please refer to:
https://gstreamer.freedesktop.org/documentation/installing/on-linux.html

Best regards,
Khoa

jsulm

@6EQUJ5 Sounds like an issue with your graphics driver. Does any media player work?

6EQUJ5

@KhoaTran-Programmer On https://gstreamer.freedesktop.org/documentation/installing/on-linux.html the instructions for Debian installation is this:

Install GStreamre on Ubuntu or Debian
Run the following command:

apt-get install ....

Which I'm not sure about. I tried running sudo aptitude install gstreamer which didn't work. Then after typing in sudo aptitude install gstreamer and pressing TAB a bunch of packages came up which I don't know which to install.

Can you clarify how to install on Debian?

jsulm

@6EQUJ5 You should install all the GStreamer plug-in packages.
But I don't think it is related to the installed GStreamer packages: if something needed is missing you will not be able to play a media file, but you should not be logged off.

6EQUJ5

@KhoaTran-Programmer The Gstreamer command line tools doesn't work (no such command exists according to terminal even with sudo). But, trying to install the Gstreamer plugins such as gstreamer1.0-plugins-base with sudo apt-get install gstreamer1.0-plugins-base tells me it's already installed.

@jsulm What do you mean "any" media player? The examples on Qt or any media player that is installed? If you mean any old media player GNOME MPlayer works.

@SGaist Aren't I doing that already? By using this version: Qt 5.8.0 for Linux 64-bit (766 MB)

jsulm

@6EQUJ5 Qt 5.8 is for sure not what Debian provides (maybe Unstable?), I guess you installed Qt 5.8 by yourself, right? What @SGaist means is: try with Qt provided by Debian.