Big CPU load at using the Camera view

When I use this simple QML example:

    VideoOutput {
        anchors.fill: parent
        source: Camera {
            id: camera
            viewfinder {
                maximumFrameRate: 30
                minimumFrameRate: 30
            }
        }
    }

I got the CPU load ~25% (where even the resolution is 640x480).

But when I use this direct gst-launch pipeline:

gst-launch-1.0 v4l2src ! image/jpeg,width=1920,height=1080,framerate=30/1 ! imxvpudec ! imxipuvideosink

I got 6-8 % CPU load (with 1920x1080 resolution).

Seems, that QtMM use non-optimal pipeline, and, even, there are impossible to configure the QtMM to use a desired pipeline (at least I did not found it in Qt documentation).