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After Effects Alpha Channels and Traveling Mattes
In After Effects:
Choose File->Project Settings...
     Select Frames, this is easier to view than timecode.

Choose Composition->New Composition...

Choose Layer->New Text  Type a word, adjust the size, make the text white.


Motion Sketch
Select the text with the Arrow selection tool at the top.  AE_selection_arrow

Select Window->Motion Sketch, you will use this to interactively animate your type.
          Click the Start Capture button
          Drag your type around the Comp1 window.

Hit the arrow playback button to see your results.


Modes
Set your Time Marker on the Timeline to the first frame.

Choose File->Import->File  to bring in an image sequence to mask into the type.

Make sure you are in the Project tab  (Window->Project if you don't see it)
Drag your movie on to the Timeline.
     Drag it below the type, see diagram below.

Go to the Mode/Track Matte section on the Timeline. If you do not see it hold down the right mouse over Parent and add Columns->Modes. You can hide Parent.

Click and hold on the button that reads None across from the movie; switch it to Alpha Matte.
Notice the text layer is now turned off.

aftereffects1.jpg


Complex Layers in Layers
Drag and drop your text composition onto the Create a New Composition button in the Project section.
     This creates a new composition.
ae-new_project

Select the New composition in the Project section.
Then select the composition in the Timeline
Choose Effect->Distort->Polor Coordinates
Click the time-vary stop watch next to Interpolation in the Effect Controls section
     This sets a keyframe.
Change the time on the Timeline
Change the amount of Interpolation
     This sets another keyframe
repeat

Window->Project will bring the Project section back


Export the Composition to Media Encoder
Select the composition in the Project section
Choose File->Export->Add to Media Encoder Queue...
Media Encoder will start

How to use Media Encoder to render a movie.