I need to add closed captioning to a short video that will be broadcast on our cable TV system. The cable system will accept MPEG-2, QuickTime MOV, or AVI/DV formats. This is in the United States, and I'm guessing that we will need both EIA-608 and CEA-708 formats. Because I am not actually producing the video itself, and I don't have it yet, I don't know whether it will be in a standard-definition or high-definition format. I am presuming the latter, but information on either could be helpful.
What software (preferably free and/or open-source) can help with this task? I have tried Google, and I have tried skimming the documentation of some of the packages out there (e.g., Kdenlive) to no avail. I can use Linux or Windows software for sure, and I can probably find someone with OS X if needed.