This should still work as long as the video and caption files are located in the same sub-folder. The caption file does not need the same name as the video file, although it would help keep things organized.
For example if the sub-folder was named "cache":
You could play back the stream as
When using sub-folders, you need to add _definst_ to the URL.
I hope this helps, but maybe I am still not sure what you are after