VobSub

VobSub is a program for extracting subtitles from DVDs, and its characteristic format consisting of files with .sub and .idx extensions. It is no longer being developed, but a program called DirectVobSub has similar functionality.

The .sub file contains the subtitles themselves, stored as they are on the DVD itself, as graphics rather than text (meaning that other programs converting them to text form need to do OCR, optical character recognition, on the images), while the .idx file is an index tying particular titles in the .sub file to particular spots in the film (designated by timestamps); the file also has some metadata related to the subtitles in the .sub file. The .idx file is in ASCII text format, with a particular structure.

The ripped subtitles are in PES (Packeted Elementary Stream) format, as they are found in the original DVD.

Format information

 * .idx format info
 * PES header info

Software

 * VobSub download (MS Windows)

Other links

 * Subtitle formats explained
 * Stack Overflow discussion
 * Wikipedia article on DirectVobSub