I'm trying to backup some family videos from old Sony Mini DVD-R and Mini DVD-RW's. Some of the discs have data stored on them (the discs are labeled and I can visually see that they've been written to) but Windows, MPF & ImgBurn all think that the discs are empty. Any ideas as to why this is happening and/or how I can grab the data?

Some of the discs are also cracked - is there any way to grab data from the unaffected areas or are they totally unsalvageable?