extract CSS from a DVD.
Project motivated by the need to recover scratched DVDs within my collection. Most DVD ripping software doesn't handle scratches well, as they either give you the option to die, ignore or retry the error.
ddrescue (from GNU) actually can work very well for this as it keeps a bitmap of what content one was able to read and then can fill in the missing pieces later, however, it doesn't decrypt data. Most decryption software doesn't decrypt ISO's with CSS scrambled sectors (though VLC and other tools built around libdvdcss can play them fine due to libdvdcss brute forcing the crypto), as they expect ISO's to be already decrypted and query the device for the content's keys instead of brute forcing the crypto.
This software decrypts the scrambled sectors in place enabling you to then extract the iso to a file system or use another ripping tool to extract the desired content from the already decrypted image.
For protection mechanisms that protect the disc by including invalid sectors, ddrescue will mark those sectors as unreadable, but it doesn't matter as they aren't needed. However. if the disc is protected with that, and it's damaged (such as scratches that make needed data unreadable), one will not be able to tell the difference.
If the disc has protection mechanisms that cause it to be viewed as a very large file system (i.e. a DVD that looks like a 100GB file system), this will remove the encryption and enable you to mount the image, but you will not be able to simply extract the contents of the images (without wasting a lot of space). Tools that understand the IFO structure are neccessary to extract the correct files.