Bit-rot
I’ve been trying to convert a load of old DVD-R’s to AVI files as its easier to have a fileserver full of movies than to search through hundreds of discs. Its taken days to do just half a dozen or so – mainly due to bit-rot and scratched discs, but also due to old versions of DVDShrink3 and CloneDVD2 corrupting the disc structure, so programs like CloneDVD Mobile and DeVeDe are not only taking 2-3 hours to do the transcode, but also hours to read the bloody discs and correct the structure.