Pixels, videoGrabbers, pointers and references

a pointer to a reference doesn't make really sense, when you dereference (take a pointer) of a reference you are just taking a pointer (the memory address) of the original object,

with the pointer to ofPixels, you can still do:

(*pixels)[i]

but to make the syntax easier you can just do:

ofPixels & pixels = *pixelsArray[0];
pixels[i];