I’ve got a little egg on my face but the problem turned out to be that -R discs have issues but +R discs burn just fine. I had the +R discs laying around and tried one and it worked just fine. I’m editing on an iMac bought in 2010 but the -R discs in question always worked flawlessly in an 2009 MacBook Pro for stills while the +R discs wouldn’t work at all. I thought the DVD burner in these machines was adaptable to any disc. Don’t understand why. I learned quite a bit about codecs and Compressor 4 in the processor so I guess it wasn’t wasted time. Just wanted to share.