I've been messing with Blu Ray playback on MythTV lately. Although I haven't tried a big seamless branching movie yet (I have Meet The Robinsons), the movie I have been messing with, Star Trek Nemesis, seems to have lots of different titles to chose from. The first in the list is the main movie, and further down the list I found one that seems to be a series of deleted scenes. Subsequent titles are then the individual scenes again. I know quite often on DVDs and Blu Rays in the deleted scenes part of the menu, you can select individual scenes to see, or you can "play all." I would guess that each of these scenes is a seperate .m2ts file in the STREAM folder, so play the "play all" title would be similar to playing a seamless branching Blu Ray movie. That being said, it did work for me. I will try to dig out Meet the Robinsons later tonight, and I'll see if that one works too.
I'll share with you a few of the problems I have noticed playing back Blu Rays:
1. When the main movie was over, Mythfrontend crashed. Because I run Mythfrontend by using the "startx" command, I then found myself back at the command line. Most users would probably just see their desktop again. Ideally, when the movie was over, it should prompt you with the list of titles so you could continue to watch another one, or hit escape to back out of that movie and choose something else to play. I don't know how it is supposed to work, but it was kind of annoying when I was trying to watch all the different titles, since I had to catch it before the title ended, or risk a crash.
2. The bookmark feature does not remember the title you were watching. I tried bookmarking one of the bonus features, and when I restarted the movie, it asked if I wanted to start over or resume from bookmark. When I chose to resume, it resumed to the correct time, but on the main movie, and not the title I was watching.
3. Starting the movie takes quite a while, I'd say at least 10-15 seconds. This could be because both my backend system (Pine Trail) and frontend system (Ion) are Intel Atom based. I need to check and see if one of them has high CPU usage during this time.
4. Forced Subtitle tracks do not work. I tried the movie Iron Man, and the forced subtitle track did not play. When I enabled it manually through, it worked, so MythTV does support playback of Blu Ray subtitles. I seem to recall that the subtitles would stay on the screen too long though.
5. Interlaced VC-1 movies don't work. These are quite rare, and the only one I have (George Carlin: It's Bad For Ya) didn't work.
6. HD-DVDs don't work. I ripped an HD-DVD using the same method as my Blu Rays and it did not recognize the folder structure like it did with the Blu Rays. I could enter the folder, find the .EVO files and play them, but no structured playback like with Blu Rays. Probably not a big deal for most people, and I don't think they even claimed HD-DVD support, but I just wanted to mention this since I did try it. On the plus side, when I used eac3to (in Windows) to process my test HD-DVD, I created an MKV file with the original VC-1 video track, and original E-AC3 audio track. Mythvideo was able to play the resulting file just fine, so it does support E-AC3 audio playback from MKV files. Media Player Classic (build 2099) in Windows had broken audio when playing this same file, so that's definitely a win for MythTV!
So it's not perfect by any means yet, but it's a great first step. This particular movie has Dolby TrueHD and it played that just fine. I'm just using 2 channel HDMI out to my TV's speakers right now, so I can't say for sure how accurately it is decoding the audio (16 vs 24 bit, multichannels mapped correctly, etc.). So if you want me to check anything else about BD playback on MythTV, I do have a working setup, and I'm very familiar with how BDs work.