Use .srt (subRipTile) or SSA (SubStation Alpha)

I'm pretty sure I'm correct in saying that jit.qt.movie doesn't provide any particular help to you in dealing with .srt files, but you can write a program that synchronizes a .mov with a .srt. The .srt format is just plain text and very simple to parse. I think you could build your own in roughly the following way.

Use the text object or the js object to read in the .srt file. The js object would be my choice because you could also use it to parse the file, translate the timecode into QT timescale units, etc. Load the .mov into jit.qt.movie and query its timescale units with the 'gettimescale' message. You'll need to use that value in order to convert the .srt timings into timescale units. As you play a .mov file in jit.qt.movie, you would need to continually poll its current time (in its native timescale units) by sending it the 'time' message. When the movie time equals or surpasses the start time of a subtitle, trigger the display of that subtitle, and when the time equals or surpasses the stop time of the subtitle trigger the end of the display of that subtitle and start looking to display the next one. By "trigger the display" I mean write the text of the subtitle into a jit.lcd object then composite that on top of the movie (using jit.op @op + or jit.alphablend), or another way would be to write the text into jit.gl.text2d and render that on top of a jit.gl.videoplane that is showing the movie.

I guess that's a verbose and complicated explanation. I don't have time to write an example program, so I hope it's clear. I don't think it's hard to do, but you do pretty much need to build it from scratch, I fear.