Many DVDs I burned movies onto a couple of years ago have suffered degradation and are now unplayable. Recently, I came across
CD Recovery Toolbox Free which has recovered several DVDs and rendered them watchable. It is more successful in this respect than any other data recovery software I have tried. Other software has either failed altogether or left problem areas on recovered files unviewable.
The downside is that CD Recovery Toolbox Free can be a little buggy, hanging when more than one file is selected or after it has been used a couple of times. Nevertheless, if it is used patiently it does give good results.