Subtitle ripping - how does it work?

[guipo]

I've been reading Doom9's posts and guides and I've have some questions (sorry if they are dumb...):
1) Do all subtitles ripping techniques use OCR ?
2) Are subtitles streams, like sound and video? Which format is it internally ?
thnks

[CoNS]

1) Do all subtitles ripping techniques use OCR ?It depends on what you mean by "subtitles ripping". DVD subtitles are bitmap images ("subpics") stored inside the VOB files. You can extract DVD subtitles to various formats where the subpics are kept in bitmap format, like .SUP or .IDX/.SUB.

Or you can convert the bitmap DVD subtitles to text. This will require OCR processing.

2) Are subtitles streams, like sound and video? Which format is it internally ?Yes, the subpics are located in separate subtitle streams inside the VOB files, like audio streams and the video stream.

[guipo]

Thanks for the answers.
One more basic question. So if it is a stream inside a VOB, why can't (e.g.) DVD Decrypter simply rip it as it does with other audio an video streams? Why is it necessary a specific tool like subrip for that ? :confused:

[CoNS]

DVD Decrypter and lotsa other tools can rip the subtitle streams to separate files in various formats.

Tools like PgcDemux, VobEdit and DVDSubEdit can read the VOB files and save the subpic streams as .SUP files, which contain a sequence of the bitmap images with the subtitles (subpics) along with time codes and other information about the subtitles.

SubRip (and the OCR function in DVDSubEdit and some other tools) goes a step further, as it's able to convert the text (subtitles) in the bitmap images to plain text.

[guipo]

Thank you - You've just cleared my doubts.