After a few experiments, this seams to be an efficent way of creating Blu ray back ups.
1. Rip Blu ray movie to hard drive.
2. Using Tsmuxer 1.84, browse stream folder for main movie and then make a new Ts file with the video and required sound track, 5.1 DD prefered.
If its too big to fit a single layer BD-R, procede as below.
3. Using Nero 8 with HD plugin start a new Blu ray movie project.
Load the new Ts file from Tsmuxer. Set the video standard in Nero to NTSC.
Enable smart encode. Select DD 5.1 for sound track. Select 2 pass encode if you wish (it will take a lot longer to encode).Tick 'create chapters automatically'. Do a menu if you want one, i dont bother.
Select a hard drive folder as your target.
The encoding will take hours to complete!.
If you leave Nero settings to auto it will produce an Mpeg2 video stream.
If its a very long movie, select custom and choose Mpeg4.
This will take even longer to encode. The finished video will be 29.97fps interlaced. Ive had good results so far.
Hope this is helpfull!