Bitmap sublitles - why?

[krypton22]

I wonder, what's the actual reason bahind making bitmap subtitles a part of the DVD/HD-DVD/Blu-ray standard as opposed to text (vector) subtitles, which offer smaller size and better comfort? Is that only an effort to make subtitle stream ripping more difficult or is there any other (rational) motive?

[Sir Didymus]

The reason comes from the need is to support foreign languages and idiograms using symbols of whatever alphabet, adopting fonts and typographic variations of the maximum generality. Only graphics representations are sufficiently general for this purpose. For instance Klingon subtitles are fully supported by the DVD specs :-)

In addition, subpictures may be used to create graphical effects and complex animations. See for instance Spiderman 2 & 3. This set of capabilities goes much beyond the simple support to textual subtitling...

[krypton22]

Thanks for your input but... :)
Well, how difficult would it be to include one pan-unicode font or a few supporting the main codepages - it would still take up lesser space than the current bitmap streams. As nobody I know really understands Klingon (though I bet there are geeks that do), those subtitles would quite surely be made as forced anyway. As for the graphical effects, be honest and admit how many have you seen on a DVD in your entire life and how useful/entertaining have they proved to be? I'd rather have the power to change the font size/color instead.

[Sir Didymus]

...it would still take up lesser space than the current bitmap streams...

Please consider in the DVD specs the actual coding of the graphics content in the VOB files is just 4 colour (2 bits) Run Lenght Encoded. So, the pictures are compressed, and the encoding scheme is quite efficient; no uncompressed bitmaps are actually present in the sub streams... The overall size of subpicture streams for one hour and half of movie is typically of few MB. Very rarely they take more than ten MB...


...how useful/entertaining have they proved to be?

The point is that the specifications allows much more general features and complex animations respect to what is actually exploited... Let's leave some space to the fantasy of the DVD authoring houses and authors for including interaction features in their products...

Cheers,
SD