Apple has alerted users of Final Cut Pro and Final Cut Express to a problem involving FileVault encryption in Mac OS X 10.3.

The company advises users to "keep media and capture preferences outside of your home directory if you use FileVault and Final Cut Pro or Final Cut Express".

The support document explains: "Capture to your home directory puts an unnecessarily large strain on the computer's microprocessor, and this could cause the applications to drop frames during capture, or skip them during playback."

Apple advises: "For best performance, capture video to a drive other than your startup disk. If you are working with a relatively low data-rate format such as DV, or if you must use your startup disk, make sure your scratch, cache, and media files are outside of your home directory."

The company has issued instructions for changing the scratch and cache settings. Apple recommends users "choose a location outside of your home directory for all capture, render, and cache files. For example, the root level of your drive or a different drive if available".

Apple warns that "media inside your home directory can cause dropped frames on playback if FileVault is turned on".

FileVault is a feature of OS X 10.3 that allows users to secure files to the home directory by encrypting them. Panther-users have reported problems when enabling FileVault, which have lead to reset or destroyed data in Safari, Address Book, Mail, Keychain, and the Dock.