Exporting a Self-Contained Movie Without Recompressing the Media
If you choose to export a self-contained movie, you have the option to not recompress
the media in your clip or sequence. If you deselect the Recompress All Frames option
and choose Current Settings from the Setting pop-up menu, Final Cut Pro simply
copies frames from existing media files into the new file with no recompression. This is
a convenient way to export your media without subjecting it to recompression
artifacts. However, any media that must be created from scratch, such as a transition
between two media files, must be recompressed.
The option to turn off recompression is unique to the Export QuickTime
Movie command and the Batch Export command. If you choose the Export Using
QuickTime Conversion command, every frame is always recompressed.