Actually I don't really see much sense in burning YouTube HD videos to Blu-Ray. converting videos. Nowadays you can use a cheap network media player like WD TV Live that allows to play videos from a USB Flash drive, portable hard drive, or even from your network.

Why do you want to burn your YouTube HD videos to Blu-Ray? Where do you plan to watch them?

Related thread:
Burning HD (1080p) FLV to Blu-Ray with high quality?