Getting rid of 'forced' subtitles

[froboz]

Scandinavian dvd's often have subtitles 'forced', meaning that you can not watch them without showing subtitles in some language. Mostly there is a choice between danish, finnish, norwegian and swedish. I was trying to back up one of them - Egmont "Nordisk Film" edition of "The Fan". My goal was to be able to watch the movie without subtitles, but also to be free to turn them on or off while playing. No matter how I did with dvd shrink, the subtitles were always shown. Using Ifoedit, I found no prohibited user operations or pgc commands that forced the subtitles upon you. The forcing of the subtitles were not using any ordinary method of dvd authoring, as they are often discussed in these forums. This is not strictly about "forced subtitles". Instead I found that there is some trick used in the subtitles themselves. If you use Vobedit to demux the dvd and then reauthor it with Ifoedit, you still can't watch it without subtitles. The raw material after demux is m2v- ac3- and sup-files. I conclude that the subpictures in the sup-files must use some trick. I would really like to know how they do it - probably with some control code in the sup-file, but documentation about sup-files or control codes for subpictures is hard to find. Finally I found a workaround. When reauthoring the dvd I add a dummy (empty) sup-file, which I made with Srt2sup. This is a well behaved sup-file, and not one of the evil bastard supfiles from hell. It will allow you to watch the movie without subtitles. Still, you can add any of the original subtitles that you want when authoring the dvd.
So, there is obviously some way for subpictures to set a flag that makes it impossible to turn them off. If anyone knows more about this, I am very curious.
I should add that there are many dvd's that behave like this, not only scandinavian. The method used to force subtitles upon us may differ.

[Dimmer]

Whether subtitles are forced or not is set separately for each subpicture screen within the VOB files. Here you can read about the structure of the subpicture packs.

If you're re-authoring a DVD, there are two ways to get rid of forced subs. One is to use an empty .sup stream, as you've already found out. Another is to rip the subs into BMP images with SubRip for example and add them back using MaestroSBT. However, this would require professional authoring software like Scenarist or Maestro. There you can set the forced flag on and off as required.