[Anujit Sarkar]

If I get this correct,
Click on the clips, go to Motion tab on your Viewer. On the Scale option Insert a Keyframe by pressing the Round button and set a scale for that point (0 to 1000). Then set another point selecting the Keyframe and set another scale.
For Instance if you start with 10 at the first point and 90 at the end point, the clips will gradually increase the size of the clips. with this method you can also change the position, color and lot of other style of the clips.
Thanks