1. A computer implemented method for multi-mode video event indexing, the method comprising executing on a processor the steps of: applying background subtraction to video input images from a video stream input to detect foreground object activity as a difference between current frame image information and static information of a contextual background of the video input images from the video stream input; determining a first level of density of the foreground object activity detected with respect to the video input images from the video stream input relative to an entirety of the image at a first time; determining a second level of density of the foreground object activity detected with respect to the video input images from the video stream input relative to an entirety of the image at a second time that is subsequent to the first time by a stability time period; selecting from a plurality of video analytics modes and applying an object tracking-based analytic mode to the detected foreground object activity of the video input images to track a foreground object, in response to neither of the first level of density and the second level of density meeting a threshold density value, and in response to the first level of density meeting the threshold density value and to the second level of density not meeting the threshold density value; and selecting from the plurality of video analytics modes and applying a non-object tracking-based analytic mode to the detected foreground object activity of the video input images to determine object movement from extracted foreground object appearance attributes without tracking the foreground object, in response to the first level of density meeting the threshold density value and to the second level of density meeting the threshold density value.