SubNamer is a free software available with Windows, which allows you to rename subtitle files (single or multiple files), which is very useful when working with a large quantity of files. In order to do that, you have to specify the source repertoire, the name format, define the subtitle file extension type (srt, ssa, sub, etc) and video type (AVI, MP4, MPG, WMV etc).

The files are then automatically renamed/converted.