ExtSub is an utility which extracts and decodes subtitle data from VOB files.
infile= The VOB file from which to extract subtitles.
videofile= A file to which to write MPEG 2 video stream data.
(optional, highly experimental)
subname= The prefix of all subtitle files (see below for
details on the individual files).
convscript= An optional shell script, which will invoke
ImageMajick's "convert" utility to turn raw subtitle
image files into TIFF files.
id= The optional ID of the subtitle stream to be extracted
(default is 0). The specification allows IDs 0-31.
Each subtitle caption in the source file generates 3 output files with the suffixes ".gray", ".sub" and ".info".
The .gray file is a raw 8bpp bitmap image of the caption. DVD subtitles however are only 2bpp. in order to see anything with the naked eye using a program such as Imagemajick's "convert". it will probably be necessary to use the Enhance->Normalise function.
The .info file is a text file containing information about the caption, such as its resolution and and alpha channel data.
The .sub file is the raw data as extracted from the VOB source. Details of its syntax is available from http://sam.zoy.org/doc/dvd/subtitles/