This clip is a more zoomed-out shot (about x2 magnification) taken lower down the glass. You can see bubbles nearer you going down, and bubbles further inside the glass are going up (more easily seen at the bottom of the picture). Different rates of flow, waves and vortices can all be seen. At about 7 seconds into the clip, a wave of liquid (no bubbles) pushes its way in from the top, forcing bubbles out of the way, and dragging some bubbles in its wake. These are the waves that are easily seen with the eye when looking at a settling pint of Guinness, and which give the impression that everything is moving downwards.