Re: 1.0-9746, 1080i output and interlaced video
After more testing, I've decided that the Dolby Digital problem is purely coincidental and not related to XvMC. Apparently, my local ABC affiliate is having problems with its digital channel's audio. Other channels work fine in Dolby.
However, XvMC is still a problem, and I've found a (temporary) solution in software by utilizing libmpeg2 and linear blend. It's not the best visually, but it's smooth. Until XvMC is working for me, it'll have to do.
As for my XvMC setup, Observer64 may be on to something. I had followed other instructions that said to make a text file at /etc/X11/XvMCConfig that contained one line of text "libXvMCNVIDIA_dynamic.so.1". A symbolic link would be a slightly different animal, and so I will try that and report back.