I swear it's for comedy not piracy

August 26, 2007 6:22 PM

How would I add a subtitle file to a dvd?

Suppose I have a movie DVD that I own. I want to make a copy of this disc, but replace one of the subtitle files with my own .srt subtitle file, ideally changing as little as possible outside of that. What's the best/easiest way to go about doing that, that it might be played on standard DVD players?

posted by kafziel to computers & internet (10 comments total)

If you're looking for free stuff, you would probably need some combination of VobSub and VirtualDub
posted by jeremias at 6:31 PM on August 26, 2007

Wow. I just want to say this seems like a perfectly genius comedic idea.
posted by niles at 6:59 PM on August 26, 2007

Just to make something clear: there is no "subtitle file". Subtitle video tracks are included in the VOB file along with the normal video and the various audio tracks.

Yes, they're video. Subtitles are not encoded as characters. A subtitle video track is 2 bit planes. You get to define three of the colors with a palette, and the fourth color is automatically transparent. During playback, if subtitles are enabled, the subtitle video is layered on top of the normal video, which only shows through on pixels which say "transparent".

A subtitle program has to render the text using some font. Experience has shown that sans-serif fonts are better. Yellow lettering with a black border is probably the best color combination.
posted by Steven C. Den Beste at 7:24 PM on August 26, 2007

[The fact that the subtitle is video is the reason why you can "follow the white rabbit" on the Matrix DVD. With the proper software you can put primitive pictures in the subtitle video stream, not just text.]
posted by Steven C. Den Beste at 7:25 PM on August 26, 2007

OK, but there's also closed captioning, which is text and not graphic, right? My TV has a slough of options controlling font, color &c of closed caption data... does the DVD spec not support that? I could've sworn that I'd encountered it before, albeit infrequently.
posted by mumkin at 9:52 PM on August 26, 2007

closed captioning data also travels with the video. It's encoded in the blanking regions (old school TVs needed time to reposition the beams) - there's no way to really have it be separate from the picture.
posted by j at 11:14 PM on August 26, 2007

Mumkin, closed captioning on NTSC broadcast is encoded into the video during vertical retrace. But they don't do that on DVDs.

They can't, because the MPEG2 storage format on DVDs has nothing whatever to do with what gets broadcast on NTSC television. Instead, they rely on the subtitling mechanism, which is a 2-bit video stream.
posted by Steven C. Den Beste at 11:42 PM on August 26, 2007

(I think the confusion factor here may be that "closed captioning" does work on videotapes. That's because a videotape actually does store the transmitted NTSC video, including the video during the vertical retraces.)
posted by Steven C. Den Beste at 1:27 AM on August 27, 2007

I've done this, not from a DVD, but from an .avi with an .srt. Opening an .srt with a text editor, it's easy change just the dialog while leaving the timing alone. So, I would rip your DVD to a video file with and external subtitle file, edit your .srt, and recombine the video and .srt files with ConvertXtoDVD or DVDFlick or something. This seems easiest.
posted by glibhamdreck at 6:57 AM on August 27, 2007

To expand a little on SCDB's notes, subtitles are added at authoring time in the DVD production process. They are supplied as a control file with 4 color bitmaps (usually) - there is a bitmap for every single subtitle. The control file contains the color mapping information, and the in and out timecodes for each bitmap. This subtitle information is then encoded and multiplexed into the DVD video information at build time.

I don't know anything about .srt files, but I'm not familiar with much software that allows you to easily rip subtitles back from a DVD into their original format - programs like DVD Reauthor will do this, but also note that it only works if the video timecode is non drop frame - with drop frame video the timecodes you get are wrong and the subtitles drift. Also, if you did successfully do this, you would have to reedit every timecode in the control file and create new bitmaps for every subtitle.

On the note of closed captions, a closed caption file is simply a text document with an in point for each caption and the corresponding caption. However, the caption is encoded as a series of digits - it's not in the English (or whatever) form. So if you want to modify closed captions, you'll probably need specialist software for that too - I don't know that much about CCs, but I do know that the encoding is not simple.
posted by forallmankind at 7:33 AM on August 27, 2007