When you are ready to render your final product and add metadata to the file, inside Final Cut Pro 7

Click File => Send To => Compressor
Compressor will open and present you with the file you are exporting. In the lower right hand corner in the Inspector box.

Click the Additional Information tab

Use the Add Annotations button to add Title, Description, and Keywords
Fill in your metadata information
To complete the export process select a Settings and drag it to your file.
Then drag a Destination to your file as well.
Click Submit
You will be asked if you want to name this render/export, no need to so you can just click Submit
The file will now render and will contain your metadata. You can now sent this through firepype and we will read the metadata and use it to process your files.