pokerpoker Wrote:still, noone knows really about UMD videos. while ripping, video/audio streams can be copied, but subtitle stream cannot.

and, there is no such thing as just "PNG subtitles"
but in example, sonic scenarist subs use PNG files. this is not a DVD/UMD standard so it's not recognised by PSP.
so what is that standard? I'm stuck as i have no documentation nor example files.

It's because it isn't standard - UMDs are really Sony's proprietary stuff so they can really do what they like.  Your best bet is probably Sony's UMD Tools.

And I don't think you can get soft subs in the XMB player - at least, I haven't heard anything about it.  TTXT is the only subtitle format accepted in MP4, and the PSP just ignores that.