This how to video demonstrates the software solution Jubler to create captions and subtitles. You can download and install any one of a number of desktop captioning/subtitling programs that offer options to create and export caption files for many different media players and formats. Depending on your operating system and needs, you may wish to use another system. However, all the software and web-based solutions basically work in the same way to produce a caption/subtitle file so you may find this video is still quite relevant.
You can read the full AmbITion Scotland post about how to make online videos accessible using captions and subtitles on our website.