From DVD Faq (http://www.dvddemystified.com/dvdfaq.html):

A disc also can have up to 32 subpicture streams that overlay the video for subtitles, captions for the hard of hearing, captions for children, karaoke, menus, simple animation, etc. These are full-screen, run-length-encoded bitmaps with two bits per pixel, giving four color values and four transparency values. For each group of subpictures, four colors are selected from a palette of 16 (from the YCbCr gamut), and four contrast values are selected out of 16 levels from transparent to opaque. Since one of the four values is usually 100% transparency (to let the video show through), only three combinations of colors and transparencies are left, making overlay graphics rather crude. Subpicture display command sequences can be used to create effects such as scroll, move, color/highlight, and fade. The maximum subpicture data rate is 3.36 Mbps, with a maximum size per frame of 53220 bytes.
----

I need an authoring program that can do subtitle effects (fade in/out in particular) for PC.
The only I know that can do that is Apple DVD Studio Pro 3 [http://www.apple.com/dvdstudiopro/specs.html] but is only for MAC.

Subtitling
* Subtitler integrated into application
* Add up to 32 subtitle streams per track
* Set position, font, size, style and color, fade in and fade out
* Enter timecode or drag in Timeline to set start, stop and duration
* Built-in title safe and action safe areas
* Use graphics in subtitles
* Import subtitles in .son, .stl, .txt, and .scr formats
* Use buttons over video
Anyone knows a dvd authoring/tool that can do that?

Also would be great if the program can handle subtitle overlaps.