Subsync is a command line filter to synchronise the timeline of subtitles. It can shift, scale and non-linearly edit the timeline. It's simple, fast and easy to be integrated to Shell scripts. It supports .srt, .ass and .ssa formats. It's written in C and standard libraries so is able to be compiled in most of Posix systems like Linux, BSD, Cygwin, etc.
I had a couple of old TV shows and out-of-sync .srt files searched from websites. I knew the structure of .srt was quite simple so theoretically a small filter program can do the trick: filter out the time stamps, do some primary school-time mathematics, output back to the stream. To my surprise I couldn't find a command line tool to do it properly. Something were either too fancy with a heavy GUI interface, or too poor written by Shell scripts to do the basic calculation, especially to scale the timeline. Finally I decided to write one for my own needs. It might be reinventing the wheels. But come on, it costs only a handful hundred lines and a Sunday morning.