subtools is a port of DivX Subtitles MiniTools, command-line
tools for movie subtitles in SubRipper format (.srt files).
"srtshift" can adjust the subtitles by shifting them to the
beginning or to the end. "srtrate" does the same by changing
the supposed frame rate.

It's in early stages of development (and have been there for
a few years now), but it does its job well.