First, create a new layer. Stack the new footage of top of the old.

In Final Cut, right-click on the top layer and choose Composite Mode>Difference. In After Effects, use the layer’s drop-down Mode menu.

Your footage will take on an inverted and somewhat psychedelic appearance. But here’s the great part: when the two versions are perfectly aligned, they will cancel each other out and your Viewer will become black.

Credit to Chad Perkin’s and his excellent After Effects CS4 Beyond the Basics on lynda.com.

To help me through this new terrain, I compiled a list of shortcuts. Try them out for best results.

View Timeline One Frame at a Time
Page up moves current time indicator one frame backwards.
Page down move current time indicator one frame forwards.

Two Ways to Select a iLayer
Type the layer number on keypad to select it.
Use command up and down arrow to shuttle through the layers, respectively.

Jump to Current Time Indicator
If you’ve zoomed in too far and can no longer find the current time indicator, hitting d will bring you back to it.

Jump to In and Out a Layer
First, make sure the clip is selected.
I will jump to the in point of the clip.
O will jump to the out point of the clip.

Set In and Out for Playback Work Area
B sets in point for playback.
N sets out point for playback.
The Playback Work Area are the indicators above the timeline that determine how much of your composition will play back.

Jump to In and Out of Playback Work Area
Shift-home jumps to the beginning of the work area.
shift-end jumps to the beginning of the work area.

Make Playback Work Area the Size of all selected layers
command-option-b

Jump to the Beginning and End of Timeline
Home key jumps to the beginning of the timeline.
End key jumps to the end of the timeline.

Transform Property Shortcuts
S show scale
T show opacity
A show anchor point
R show rotation
P show position

See More than One Transform Property at a Time
Hold down shift while hitting another keyframe shortcut.
For instance, if the scale property is currently displaced, pressing shift-r will show the scale and the rotation property.

View Keyframes
U shows all properties that have key frames applied.
UU shows all values that have been changed from their default.

Insert Keyframe Shortcuts
option+transform property shortcut key will place a keyframe in the timeline for that attribute.
For instance, option+t will insert an opacity keyframe at the current time indicator position.

Replace Footage in Timeline While Keeping the Original Keyframes
First, select track with media to be replaced.
Next, hold down option as you drag replacement footage on to selected track.
The media is replaced but the keyframes will remain intact.

Markers
Markers are added using the Layer>Add Marker menu
K jump forward to marker
J jump back to marker
Right-click to delete or lock
Drag to move
* (star key) makes marker on audio timeline

Move Beginning or End of Footage to Current Time Indicator
[ (open bracket) moves start of clip to current time indicator.
] (close bracket) moves end of clip to current time indicator.
These keys do not  change the length of the clip.

Trim Layers
option [ (option-open bracket) – trims the footage so that the clip begins at the current time indicator. Shortens the clip’s time.
option [  (option-close bracket) – trims the footage so that the clip ends at the current time indicator. Shortens the clip’s time.

RAM Preview to Hear Audio
Keypad 0