flow tracking by Davis software -- 2

There are two fluids (oil/water) where oil moves on the water surface. I am interested to find the velocity vector, changing the oil thickness with time, and plot it by using Davis software. note here, I don't use particles in the experiment but instead of particles, there are some air bubbles on the oil surface which I don't know if it is possible to track these bubbles.

video recorded 30 fps.