[Interest] QMediaPlayer on iOS output audio to loudspeaker

[xuxiang at cchar.com]

I used Qt 5.6 (commercial edition) QMediaPlayer to play a simple local mp3 file on iPhone5 and iPhone 6, both running ios 8.4.
On iphone 5 , audio output to the loudspeacker. But on iPhone 6 , audio output to the jack and I need to use a headset to listen audio output.

Then I use an iPhone 6s Plus, it also output to the jack.

And then I use an iPad Air running iOS 7 . The audio  output to loudspeaker.

My question is: how to ensure that when headset not plugged in , the audio will always go to the loudspeaker?