In recent years, Pat Besong of ITS had developed and offered a captioning tool for the Mac called "Parity." This tool has now been released as MovCaptioner from http://www.synchrimedia.com.
It is still free for Penn State users. You can contact Pat Besong (pzb@psu.edu) for information on how to obtain a license.
The cost for users outside of Penn State is approximately $40, but it does support a wide range of caption types including Quicktime, Flash, YouTube, video poscast and more.
For additional options see http://webstandards.psu.edu/accessibility/tech/audio#caption or http://www.dcmp.org/ciy/ (Caption it Yourself plus list of other tools on lower half of page).