thank you I think I am starting to slightly get my head around this!
I would like to double if i am correct about this section?
//y is set at 0 and if that value is lower than video height then add the value
for (int y = 0; y < video.height; y++){
// this sets the boundary for the loop to take place? which means the width of the canvas (but not sure how + drawPositionX adds to that because it is set to 0
int setPixelIndex = y*width + drawPositionX;
//this takes the video width and adds the section of video to that?
int getPixelIndex = y*video.width + videoSliceX;
pixels[setPixelIndex] = video.pixels[getPixelIndex];
}