I apologise for the delay in getting back to you. I wasn't feeling too great at the start of the week and I had some work to do later on.
The way I was hoping to complete the task (using VLC)doesn't look as if it will work but creating a subtitles (.srt) file should be simple enough. That would leave your videos 'softcoded', where you have two separate files for the video and subtitles (with your video player combining them together). From there I could probably work out how to 'hardcode' them (where the subtitles are actually embedded into the video file), if necessary, but that would be likely to result in a reduction in quality of the video (because the data has to be resampled).
If you still want me to have a go, please send the file (plus the instructions for the subtitling) to
[email protected], letting me know whether softcoding would be sufficient or whether hardcoding is essential.