QAudioDecoder() fails in Windows 7

[HereWeAre]

Creating a QAudioDecoder fails in Windows 7 with the error:
defaultServiceProvider::requestService(): no service found for - "org.qt-project.qt.audiodecode"

Code:

QAudioDecoder decoder = new QAudioDecoder();

QAudioDecoder decoder = new QAudioDecoder();

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I tried using Qt versions 5.4 and 5.5.1 on Windows 7 and got the error both times. The code runs fine in Ubuntu.
I have

QT       += core gui widgets multimedia

QT       += core gui widgets multimedia

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in my .pro file.