2. The computer-implemented method of claim 1 , further comprising: receiving, through the graphical interface, at a second moment during the presentation, a second selection of a second interface element of the plurality of interface elements; in response to receiving the second selection, storing second data that maps a second category, corresponding to the second interface element but not the first interface element, to a second time point at which the motion video was being presented at the second moment; and generating, based at least in part on the first data and the second data, a second tracking graphical element that indicates at least (a) the first quantity of times that the first interface element has been selected during the first time interval that includes the first time point and (b) a second quantity of times that the second interface element has been selected during a second time interval that includes the second time point but not the first time point.
2. The computer-implemented method of claim 1 , further comprising: receiving, through the graphical interface, at a second moment during the presentation, a second selection of a second interface element of the plurality of interface elements; in response to receiving the second selection, storing second data that maps a second category, corresponding to the second interface element but not the first interface element, to a second time point at which the motion video was being presented at the second moment; and generating, based at least in part on the first data and the second data, a second tracking graphical element that indicates at least (a) the first quantity of times that the first interface element has been selected during the first time interval that includes the first time point and (b) a second quantity of times that the second interface element has been selected during a second time interval that includes the second time point but not the first time point. 3. The computer-implemented method of claim 2 , wherein the first interface element is a first color; wherein the second interface element is a second color that differs from the first color; wherein the second tracking graphical element includes a first quantity indicator that is the first color and that indicates the first quantity; and wherein the second tracking graphical element includes a second quantity indicator that is the second color and that indicates the second quantity.