Were they older smack packs? If they are relatively fresh (less than 2 months old), you will not realize a lot of yeast growth with 2 packs in 2 liters of starter wort. Also, your vortex looks pretty deep, so any signs of krausen would have been pulled back down and mixed into the slurry. I'm with Bob357 on this one, turn you stir plate off for a bit and see how much settles. If you still have active fermentation, you will start to see some signs of bubbles and krausen forming. My guess is that with the initial amount of yeast cells you pitched, they will have pretty much chewed through the wort and be ready to settle out.