You can resize keyframes in Adobe Flash and you can do this for anything like images, animation etc. So to do this first click on your first keyframe and hold down the shift key and then click on the last keyframe. Now select the free transform tool and resize that as showing in the video but it only resize the keyframe on which the header currently is. So now this time right click on the keyframes and choose copy frames. Now make a new layer and hide your old one. Now select the pencil tool and draw a line and click that keyframe, press F8, name it and click ok. Now double click on that symbol and right click on that keyframe and choose paste frames. Now go out your symbol and then resize it and you are done.