I haven't seen such a thing, though you can try wading through the vast landscape that is
AVS Forums.
I think
this is the forum for HTPCs and stuff like that.
Do you want this for a TV tuner card or for DVD movies? I'm pretty sure it is program-dependent, the closed captioning, I mean. You might be able to tweak around with Graphedit, but there is a sort of steep learning curve if you're really new to playing around with filters, codecs, and stuff like that.