Apple Final Cut Pro 7 - Manual (Page 1484)

If a film or video was shot to be exclusively viewed in a widescreen venue, this technique
is usually the best approach for downconversion. However, this method makes poor use
of the already lower resolution of an SD 4:3 frame, because many lines are not used at
all.
1080 to 480
720 to 480
To letterbox a 16:9 clip within a 4:3 sequence
1 Create a sequence with a 4:3 aspect ratio. For example, choose the DV-NTSC or DV-PAL
Easy Setup and then create a new sequence.
2 Drag a clip with a 16:9 aspect ratio to the sequence.
If a dialog appears asking if you want to conform your sequence settings to your clip,
click No.
The 16:9 sequence clip is now scaled to fit in the 4:3 sequence and appears letterboxed.
For more information, see “Scaling Images and Video Clips to Match a Sequence.”
1484 Chapter 86 Working with Mixed-Format Sequences