Dvds

Unless you want to spend big money sending them out to a data recovery service, they likely is no solution.

Copy the files in small batches. When you hit an error, copy the files that were in that batch one at a time. One or more of them will probably not be readable. That will be because all or part of it was store on a part of the disk that has now oxidized or otherwise been damaged.

If you're copying in the Finder, don't try to copy all the files in one go: this can cause the process to jam up. Do it in moderate sized batches.You could also try making a disk image (if Disk Utility still does that) of the DVD: that would produce a mountable image which would be much faster to copy from (thougth of course making the image will take some time, but isn't as likely to fall over).

Do you mean bought DVDs? These are copy protected - nothing will copy them.

If these are DVDs you've made yourself, copying the video.ts file into iMovie may enable you to save it out from there in a chosen format.

Contrary to popular opinion, recordable optical disks are not a permanent storage medium.

If stored in "ideal conditions", they should last 100-200 years...

Unfortunately, achieving those conditions is virtually impossible in the real world.

In the real world, recordable optical disks will degrade and begin to become at least partially unreadable in 5-10 years.

It's likely the problem you're having is the disks themselves.

Commercial DVDs?