Re: Is the ycbcr output using a rgb conversion?
The desktop itself is always RGB 0..255 range. I doubt a native YCbCr desktop is possible under X.
I believe the default VDPAU color-space conversion matrices expand video to PC range (0..255). However, you can use a custom matrix to convert to CE (16..235) range instead if you want. That's probably what the MythTV/XBMC options are doing, so it's all rolled into 1 conversion during YCbCr->RGB post-processing rather than 2 conversions.