The Soundtrack Pro installer does not install the QuickTime MPEG-2 Playback Component, which is required for MPEG-2 file playback and the Compressor Preview function. If you need the ability to import and playback MPEG-2 content, you can purchase the downloadable QuickTime MPEG-2 Playback Component, which is available from the Apple Store.
Final Cut Studio also includes the QuickTime MPEG-2 Playback Component.