I have recently received 20 finalized noncommercial -r dvds of an unfamiliar brand, but which are labelled "DVD-R 120 min/4.7 GB for Data & Video 16x." I have two standalone SD dvd players (one Sony, one Philips), both of which normally work with dvd-r without problems. However, neither one can do a thing with any of these particular dvds. The Sony says "cannot play this disc," and the Philips says "playback may not be available on this disk."
However, I also have a Mad Dog burner, and it can process the dvds. Not only can it process them, it can also copy them onto -r dvds that the standalone dvd players can play. The Sony and the Philips understand +r as well as -r; the Mad Dog also knows dvd-ram.
Why is this happening?