from Andrew Balis’ excellent tutorial “Getting the Most Out of Match Frame In Final Cut Pro HD” on kenstone.net
(if you haven’t spent some quality time with the tutorials at kenstone.net you should really take a look)
How to Match Frame From Subclips and Merged Clips
When you Match Frame from subclips and synced or merged clips, your Match Frame options are extended.
When you sync video and audio clips in FCP, and subsequently use the new merged clip in a sequence, you have two different Match Frame options. You can match back to the merged clip, or back to the original video and audio sources used to create the merged clip. In other words, you can go back to the “child” or “parent” clip. It’s the same with subclips. You can Match Frame back to a subclip, or back to the original source clip used to create the subclip. This is great when, for instance, you’re working with a subclip and want to find another portion of the same media used to create that subclip.
To Match Frame back to the subclip or merged clip, the command is the same as a standard Match Frame:
Press F
or
Match Frame button in Canvas
or
View menu > Match Frame > Master Clip
To Match Frame back to the parent clip, do either:
Command/Option/F
or
View menu > Match Frame > Source File