BDSup2Sub is a tool initially to convert captions demuxed from a Blu-Ray transport stream (M2TS) into the DVD VobSub format (SUB/IDX) used by many DVD authoring tools - hence the name. Many more features were added over time as was support for other formats. So in the meantime the name seems a little inappropriate. In a nutshell, it's a subtitle conversion tool (for image based formats) with scaling capabilities and some other nice features.

Supported Formats
1. Blu-Ray SUP: Import (since 1.0) and Export (since 1.6)
2. Sony BDN XML: Import and Export (since 3.3.0)
3. HD-DVD SUP: Import (since 1.9)
4. VobSub (SUB/IDX): Import (since 3.5.0) and Export (since 1.0)
5. DVD-SUP (SUP/IFO): import and export (since 3.9.0)

Features
1. add a fixed delay to all timestamps (since 1.0)
2. perform a frame rate conversion e.g. for pal speedup (since 1.0)
3. synchronize time stamps to output frame rate (since 2.0)
4. edit times and position of each caption (since 2.3)
5. control all features (except editing) from the command line (since 1.7)
6. move all captions inside or outside a given area (since 2.7) or horizontally (since 3.9.6)
7. scale up/down with a variety of filters (from bilinear over bicubic to Lanczos3 and Mitchell) (since 3.4.0)
8. edit "forced" flags (since 3.6.0)
9. exclude single captions from export (since 3.6.0)
10. erase rectangular regions of a caption (since 3.6.0)
11. scale captions independently of screen size (since 3.7.0)
12. automatically remove fade in/out from imported subtitle streams
13. export the target palette in PGCEdit text format (RGB values 0..255) (since 3.9.0)
14. edit the imported DVD palette when input is either VobSub or SUP/IFO (since 3.9.1)
15. edit the frame palette and alpha values when input is either VobSub or SUP/IFO (since 3.9.3)
16. set/clear forced flags for all captions (since 3.9.9)

BDSup2Sub only supports image based subtitle streams. It doesn't (and probably won't ever) support text based formats as SRT or SSA. Note that to convert image based subtitles to text based subtitles would need an OCR (Optical Character Recognition) approach which is beyond the idea of converting between image based formats. There are other tools like SubRip and SupRip to convert image based subtitles to SRT. For the other way round (SRT to BD-SUP), you may have a look here.
While importing HD-DVD SUPs is supported, BDSup2Sub can't export this format currently - and with the commercial death of HD-DVD I think adding this feature would be a waste of time.

Requirements:
* Java Runtime

How to use BDSup2Sub?
With the Java runtime installed, the JAR can be started by double clicking on it. Alternatively, you can start it from the command line via:
Code:
java -jar BDSup2Sub.jaror in Windows if you don't want a open CMD box:
Code:
javaw -jar BDSup2Sub.jar

The license of this software is Freeware, you can free download and free use this video converter software.