With BD Rebuilder can you now shrink and make a complete backup of your Blu-ray movies to DVD sizes(4.37GB or 7.95GB) or to single layer Blu-ray Disc(23GB). This is a very very basic guide, which will show you how it can be done.

Please remember that BD Rebuilder is still in BETA mode so it will NOT work on every system and with every Blu-ray movie yet.

Tools required

ffdshow (free)  – http://www.ffdshow.info/
avisynth (free)  -  http://sourceforge.net/project/showfiles.php?group_id=57023
Haali Media Splitter (free) – http://haali.cs.msu.ru/mkv/
BD Rebuilder BETA (free)  – http://forum.doom9.org/showthread.php?t=143716
AnyDVD HD ($111, required for commercial Blu-ray movies)  – http://www.slysoft.com/en/download.html?aid=50081
Imgburn (free, to burn the shrinked Blu-ray on DVD or Blu-ray media)  – http://www.imgburn.com/

Preperation

Install ffdshow, haali media splitter, avisynth and AnyDVD HD.
Extract the BD Rebuilder files to a folder.

Guide

Launch BD Rebuilder.

Choose your Blu-ray Drive or the folder with the Blu-ray files.

Set a working path (you need a lot of HDD space, ~15-50GB!!!).

Under Mode choose if you want to backup the entire Blu-ray(Full Backup) or just the Main Movie.

Under Settings->Options choose the output file size, DVD-5(4.37GB), DVD-9(7.95GB) or BD-25(23GB). Bigger file size = better video quality but if you just keep the main movie and ONE audio track you still can get pretty good quality on a DVD-5.

Under Settings->Setup can you set what audio and subtitle tracks you want to keep.

Try remove as many audio tracks possible and you will get more space for the video = better video quality. You can also set it to DO NOT convert DTS to AC3 if you want to keep the DTS track.
Backup.  

Done

You can now burn the Blu-ray Disc output folder to a DVDR or BDR and it might work on some standalone Blu-ray players. Burn using Imgburn, select Write files/folders to disc, add the folder that BD Rebuilder made and Imgburn will adjust Blu-ray settings correctly.

Problems

Be sure that you have installed a newer version of ffdshow and all the other required tools, haali media splitter and avisynth.

And, BD Rebuilder is STILL in BETA so it will NOT work on every system and with all Blu-ray movies. So wait for new releases if you get any problems.