I had tried VLC - it thought the DVD's empty, too.
I no longer have the DVD's. They've been sent off to a firm that can supposedly read old media.
But I think the DVD's might actually be empty. I looked up the lifetime of DVD+R, and there were two types. One had a lifetime of 5-10 years, the other a lifetime of 20-50 years. I don't know which I used, but if it was 5-10 years then it's quite possible nothing is left.
I thought I was transferring videos to a more permanent and more convenient media. Maybe not.
--Percy