Non consistent default multimedia settings when setting null properties

QAudioRecorder (QMediaRecorder) api use audio (QAudioEncoderSettings) and video (QVideoEncoderSettings) settings.
Their documentation state then any empty/null passed values would allow the backend to automatically choose appropriate default.
On my Linux/X11/gstreamer distribution, the audio default settings are:

Input: default:
Container: video/quicktime, variant=(string)3gpp
Codec: audio/AMR
Sample Rate: -1
Quality: 2

But, if i change the properties to something other and then decide to back to default (using null strings or -1 etc), then the new default are not consistent, resulting to those settings:

Input: default:
Container: video/x-flv
Codec: audio/x-adpcm, layout=(string)dvi
Sample Rate: -1
Quality: 2

 This is problematic and not reliable.

Also not that those are audio settings of a QAudioRecorder, and the supported container formats return both audio and video containers.. quite annoying.

One would expect that in this inherited class only audio container be reported.

More generally, it would even make more sense to have both supportedAudioContainers and supportedVideoContainers instead to make parity with the codec helpers.