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Fade out sound

  • Hi all,

    I have been a Qt developer for 5 years and C++ for developer for 12 years but never really did any audio programming. For a big project I am working on 2 multitouch applications. One of which needs basic audio support, looping an audio file, being able to stop it at any time with a fadeout. I was hoping to use Phonon for this but it doesn't seem to work with Mingw. Since I want to use the same Qt SDK for both apps and I already finished the other app using Mingw, I am a bit puzzled how to get the audio working without setting up a separate Visual C++ environment for the second app.

    I looked at Qt multimedia classes, this could be an option, but I found no support for fade out. Any suggestions? I have limited time on this but the audio support I need is so simple, yet trivial part of the app experience.

    Regards, Henk

  • Thanks, but that appears to be available in Qt Mobility only?! My apps are desktop apps running on windows 7

  • Qt Mobility is not only for mobile platforms. It also contains some support (limited afaik) for desktop platforms

  • Still I am afraid since this not an option since I have to port my already finished app to Qt Mobility. I would be surprised if it would work the same as on plain Qt, since it is a 52 inch multitouch application using heavy QGraphicsView stuff. But thanks for the effort.

  • all you need is link QtM to your app and start use it, there is no needance for rewriting

  • Okay, that would be cool. I will look into it. Thanks!

  • I'm having problems getting Qt Mobility to work. First I thought it was because I was using Qt SDK 2010.05. So I installed the latest SDK (1.1.2) from Which claims to contain Qt Mobility version 1.1.3. However after installing I created a simple app from Qt documentation using QMediaPlayer, see

    If I try to compile it complains about the following:

    #include <QMediaPlayer> main.cpp:2:24: error: QMediaPlayer: No such file or directory

    QTM_USE_NAMESPACE main.cpp:6: error: expected constructor, destructor, or type conversion before 'int'

    I must be missing out on something. Should I build Qt Mobility myself. I even can't seem to find the source files for it in the SDK directories :-s

  • AFAIK desktop Qt in QtSDK doesn't contain QtMobility. You have to build it manually or use one precompiled (if you use some package-based linux distro it will be easy to install it from repos).

  • It does contain it. The create project wizard even supports creating a mobile project. Which still feels weird since I am targeting a 52" inch desktop environment ;-)

    This is the .pro file created (and my changes):


    Add files and directories to ship with the application

    by adapting the examples below.

    file1.source = myfile

    dir1.source = mydir

    DEPLOYMENTFOLDERS = # file1 dir1

    symbian:TARGET.UID3 = 0xE80DF1B4

    Smart Installer package's UID

    This UID is from the protected range

    and therefore the package will fail to install if self-signed

    By default qmake uses the unprotected range value if unprotected UID is defined for the application

    and 0x2002CCCF value if protected UID is given to the application

    #symbian:DEPLOYMENT.installer_header = 0x2002CCCF

    Allow network access on Symbian

    symbian:TARGET.CAPABILITY += NetworkServices

    If your application uses the Qt Mobility libraries, uncomment

    the following lines and add the respective components to the

    MOBILITY variable.

    CONFIG += mobility
    MOBILITY += multimedia

    SOURCES += main.cpp mainwindow.cpp
    HEADERS += mainwindow.h
    FORMS += mainwindow.ui

    Please do not modify the following two lines. Required for deployment.




    And here is my main.cpp:

    #include "mainwindow.h"
    #include <QApplication>
    #include <QMediaPlayer>

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

    MainWindow mainWindow;
    return app.exec();


    And it does not compile for previous posted reasons!

  • Qt Creator is only part of Qt SDK and another part is Qt library itself. Your errors really looks like QtM is missing, aren't they?

  • Do you have
    #include <QtMultimediaKit>
    and more importantly, did you select Qt Mobility APIs in the Updater?

  • Yes, QtM appears to be missing. But when I go this url it says QtM is part of the SDK:

    That's also claimed on this page, from where I downloaded and installed the SDK:

    Check these screenshots from my system for more details:

  • It can be part of mobile libraries (symbian, maemo), I'm not sure on this btw (I'm using mostly selfbuilded Qt or Qt from my linux repo).

  • Try copying the mobility.prf from QtSDK/Simulator/Qt/gcc/mkspecs/features to QtSDK/Desktop/Qt/gcc/mkspecs/features

    EDIT: This might not work. Don't be disappointed if it doesn't.

  • Okay, thanks for your efforts anyway :-)

  • I did. Same errors after reloading and rebuilding the project.

  • Finally I succeeded achieving this in Phonon on Windows 7. I just adjusted the volume level to create the fade out.

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