My iMac is reading recorded DVDs as blank
I am using HighSierra on a 2011 iMac with built-in optical drive. Recently it will not play DVDs. When I insert a recorded DVD, it usually tells me it is a blank disk. Occasionally it will recognize the DVD but play it with sound but no picture. The CD function still seems to work.
iMac, macOS High Sierra (10.13.2)