My mother is completely deaf without her cochlear implant, so closed captions and subtitles on DVDs are standard fare in our house. However, when I make a home movie, I haven't always had a way to subtitle it for her. You can make a video with captions that are part of the video itself, but I could find no way to turn them off -- until I found SRT files and learned how to author a DVD with them using open source tools.