Motion detection to trigger samples

Hi all,

I'm trying to create a patch where I can triggers samples when motion is detected on a line. Similar to the concept in the video below. The end goal is to trigger splashing sounds when people walk by the webcam so it sounds like you're walking on water.

I've started out with the patch I have here (will increase the grid size later) but hit a snag when getting the data out of the matrix. Maybe this isn't the best way of doing it so I'm happy for suggestions.