DirectVobSub (formerly known as VSFilter) is a software add-on for Microsoft Windows (a DirectShow filter) that is able to read external subtitle files and superimposes them on a playing video file.
[1][2][3] DirectVobSub/VSFilter were formerly part of a whole application known as VobSub which was also able to extract subtitles from DVD Video and create text-based subtitles, without ripping the DVD to a file first.
VSFilter was a part of the guliverkli project on the SourceForge web site.
The guliverkli project also includes the ability to extract subtitles from a DVD via the vobsub ripper program.
DirectVobSub is also capable of extracting subtitles from a DVD without ripping it to a file first.