Apple Final Cut Pro 6 - Manual (Page 1772)

Chapter 21 Exporting Still Images and Image Sequences 289
III
Each file of the image sequence is named in the form of “Filename 001.ext,” where
“Filename” is the name you gave, the number (001) is the number of the frame, and
“.ext” is the filename extension indicating the format.
A file is saved for each
frame of video.