How to design a custom videoOutput?

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The videoOutput I mean is
@
Rectangle {
width: 320
height: 240

    Camera{
        id: camera
    }
 
    VideoOutput {
        id: videoOutput
 
        anchors.fill: parent
        source: camera
    }    
 
    GammaAdjust {
        id: gammaAdjust
 
        anchors.fill: videoOutput
        source: videoOutput
        gamma: 0.5
    }
}

@

How could design the videoOutput by myself?
Maybe this is the fastest and easiest way to save the
image after postprocessing,thanks

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I tried grab() function before, but this solution can't work on android,it will crash
I find through the document and exmaples but have no clue of how to get the buffer of videoOutput, safe the result after postprocess or create my own videoOutput