Trouble playing MP4 videos under Fedora 21 -- Gstreamer thinks a codec is missing which is actually installed

[Jonathan Ryshpan]

MP4 videos played OK under Fedora 20, but when I attempt to play one
under Fedora 21, I get a popup from Dragon Player (KDE's default video
player).

        Dragon Player requires additional plugins for this operation
        MPEG-4 AAC decoder
        MPEG-4 Video decoder
        
        The following plugins are required.  Do you want to search for
        these now?

When I click Continue, after a delay to download a cache, I get this
popup:

        To be Installed
        
                gstreamer1-libav
                gstreamer1-plugins-bad-free
                gstreamer1-bad-freeworl
                gstreamer1-plugins-good

But when I click Continue, after another delay to download a cache, I
get this popup:

        The package that is trying to be installed is already installed.
        
                                        Details
        
        gstreamer1-plugins-bad-free-1.4.4-1.fc21.x86_64 is already
        installed

System is 

        4 processor x86_64 (AMD)
        Nvidia Geforce 9500GT video card
        Fedora 21 with all updates
        Nouveau video driver
        KDE 4.14.3
        Dragon player 2.0

Where do I go from here?

Thanks - jon

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