Pixel subtraction on a video : how to get a serie of images ?

[kmedghaith]

Hi all,
I have some issues to make some post-processing on a video. Just to start, I would like to make a simple pixel subtraction on a video, my code looks like the following :
@
Column {
width: parent.width/2
height: parent.height

        property int itemsCount : 4
        property int itemsHeight: height /itemsCount

        VideoOutput {
            width: parent.width
            height: parent.itemsHeight
            id : video
            source: player
        }

        ShaderEffect {
            width: parent.width
            height: parent.itemsHeight
            id : image1
            property variant source: ShaderEffectSource {
                sourceItem: video;
            }
            fragmentShader: shadersFactory.simpleShader
        }

        ShaderEffect {
            width: parent.width
            height: parent.itemsHeight
            id : image2
            property variant source: ShaderEffectSource {
                sourceItem: image1;
            }
            fragmentShader: shadersFactory.simpleShader
        }

        ShaderEffect {
            width: parent.width
            height: parent.itemsHeight
            id : image3
            property variant oldSource: ShaderEffectSource {

sourceItem: image2;}
property variant newSource: ShaderEffectSource {
sourceItem: image1;}
fragmentShader: shadersFactory.soustracionShader
}
}
@

but I'm realizing that image1 and image2 are the same.

Someone knows how to get images serie from a video and put them in shaders as textures ?
Thanks in advance.

MG.