Dosen't make the grade.
I have seen an used one of these. There are many little niggles about this bit of kit from WD. I have at home a Popcorn Hour A110 HD and this virtually plays all video inc mkv + h.264 and audio files and has a lot higher spec inc Dolby 7.1. Which costs around £200. It completely blows the WD out of the water, sorry WD but it's just another product that dosen't make the grade.