Any property that’s got keyframes is usually represented with an value graph, as per the examples shown for the upcoming editor. AE and some other apps include an acceleration graph, I’ll ignore that, for now, and talk only about the types of keyframes (vertices) that occur on the bezier/straight/curved lines indicating the change over time of any value.
Timeline Property Values Vertex Types:
Right clicking on a vertex in the timeline to show a list of these types to choose from:
Equal Bezier: Both sides of the point are equally distant from the point, and exist at each end of a straight line through the point. Moving one handle moves the other, opposite handle an equal amount from the mid point that is the keyframe.
Free Bezier: As above, but the handles can be different distances from the keyframe along the same line. Moving one handle moves the other only in degrees around the keyframe, not in terms of its distance from the keyframe.
Curved Point: both handles are completely independent of each other, the handles weight the bezier from the keyframe.
Line to Left: From the keyframe, a line is drawn straight to the next vertex, only interrupted by the influence of the next vertex’s handle type, whatever it is. The other side of the vertex can be a bezier handle/point exit.
Line to Right: As above, but forward in time.
A Line Point: Both of the above on one Vertex. A corner, in other words.
These are pretty standard, and I think everyone knows what they are. But the problem is in the editing of vertices and their handles when multiple properties have the same value at the same point in time.
For this, might I suggest a solution that solves many problems of timelines in interactivity and non-linear editing of motion graphics, too.
Let the left column contain any objects/properties desired to be edited and/or seen whilst editing, and sortable, top to bottom, which, in turn, re-orders the objects on the timeline in terms of their Z depth on the graph, for the purposes of selection and editing.
Any sets of items in the left column, and their order, can be saved as a set of items to be edited, and reloaded at anytime, for future editing, contrast and consideration. Any of them can be soloed, or muted as desired without removing them from the list. Dragging them up or down moves them in the list and Z-order.
Clicking anything in the list makes it the currently selected timeline object in the graph, highlighting its line, vertices and handles for instant, easy editing.