So, I ripped all of my DVDs recently to use on a HTPC, and I ran into about 3 discs that could not be read, but would play in a DVD player. I checked and they

So, I ripped all of my DVDs recently to use on a HTPC, and I ran into about 3 discs that could not be read, but would play in a DVD player. I checked and they do not appear to be discs that are known to have any fancy copy protection. I ran ddrescue on two different DVD drives and a blu-ray drive, up to the point where 48 hours would pass with no new data recovered. This left me with still several minutes of video that was unwatchable. I solved it by spending about $12 to get used copies of all 3, which ripped fine. Any idea(s) that I could try had that option not been available?