Use this checkbox to enable/disable the keyframe-creation.
If this checkbox is enabled, all changes of the controls will create a keyframe. The value of the corresponding control will be stored within the keyframe.
If this checkbox is disabled the controls of the below sections will behave as if there is no keyframe-system applied, but only if no keyframes have been created yet for the specific control. Already created keyframes will still be active.
Lets take a look at the canvas:
The clip that actually should be seen in the canvas will be scaled down a little to make room for the additional information.
To the right of the clip a list of keyframed controls can be seen. This list describes how many keyframes have been set for each control. Controls without a keyframe will not be listed.
At the bottom we see the newly created timeline. The timeline consists of the same graphical elements we already know from the original timeline of Final Cut Express.
The yellow arrow and the vertical line represent the playhead on the timeline. Also note that the gray box at the yellow marker always is 1 frame in length.
The green line gives a graphical representation of the value of the currently selected control and how it changes for the duration of the clip. To information to the right within the timeline (here: 1 fra) tell you the timespan between two gray lines.
Within the timeline the currently selected control will be shown, its value and the upper and lower limits.