Using PGS subtitles to matte video?

[IanD]

I'm interested in matting 1080p 1.78:1 video to 2.35:1, but having the ability to switch easily between both presentations without having to encode both separately.

Is it possible to use PGS subtitles to create a variable letterbox matte overlay, or would this exceed the rendering capability of most players?

If it is theoretically possible, how would this be created? Would be useful if an Avisynth script of the required matte could be converted directly.

[Ghitulescu]

yes. (and another several chars needed to fill up the required length)

[IanD]

yes. (and another several chars needed to fill up the required length)
I don't understand what you are saying here.

[Ghitulescu]

Yes has 3 characters. The software this forum runs requires at least 5.