I´ve used MKVTools to convert 720p MKV's inte mp4/m4v that can be played on my ATV2 as well as iPhone 4 and iPad 2. However there seems to be impossible to stop watching a movie halfway through and then resume to watch it where I stopped last time. Every time I try this it always starts from the beginning. If I try to fastforward to the place I stopped last time it seems to get issues buffering the video. I get both audio and subtitles correct but the video freezes. This issue never occurs when watching HD TV-shows (22-60 min) or any SD material. First I thought it was an issue with my external HDD (where I have my itunes library located) but I synced over an HD movie to my ipad and tried to fast forward/scroll some time into the movie and it also had an issue with this. I´m currently encoding the same source file with Handbrake to see if I get a better reult this way, but it seems there is some sort of limitation when it comes to resume HD movies with our iOS devices.