Manipulate Time
After Effects is more fl exible when working with time thanmost video applications. You can retime footage or mix
and match speeds and timing using a variety of methods.
Absolute (Not Relative) Time
After Effects measures time in absolute seconds, rather
than frames, whose timing and number are relative to the
number per second. If frames instead of seconds were the
measure of time, changing the frame rate on the fl y would
pose a much greater problem than it does.
Change the frame rate of a comp and the keyframes maintain
their position in actual time, so the actual timing of an
animation doesn’t change only the position
of the keyframes relative to frames. Here’s a haiku:
Likewise, footage (or a nested composition) with a mismatched
frame rate syncs up at least once a second, but
the intervening source frames may fall in between comp
frames. Think of a musician playing 3 against 4; one second
in After Effects is the down beat of each rhythm.
Time Stretch
Time Stretch lets you alter the duration (and thus the
speed) of a source clip—but it doesn’t let you animate the
retiming itself (that requires Time Remap or Timewarp).
The third of the three icons at the lower left of the Timeline
reveals the In/Out/Duration/Stretch columns.
I mostly change the Stretch value and fi nd the four-column
approach redundant. I also never use a Time Stretch setting
that is anything but an integer multiple or division by
halves: 200%, 300%, 50% or 25%. You can do without the
columns altogether using the Time Stretch dialog (contextclick
> Time > Time Stretch).
Ctrl+Alt+R (Cmd+Option+R) or Layer > Time > Time-
Reverse Layer sets the Stretch value to –100%. The
layer’s appearance alters to remind you that it is reversed
Layer > Time > Freeze Frame applies the Time Remap
effect with a single Hold keyframe at the current time.
