I have been using MKVtools for extracting PGS .sup subtitles from mkv files which I then convert to .sub using BDSuptoSub which Handbrake can use for forced subtitles. I really like MKVTools for extracting. The problem is MKVTools doesn't seem to be able to merge a .sub back into the mkv and I have to use yet another program to accomplish this. Is it supposed to be able to do this? And can it add them to an m4v file as well?