Traveller said:

Oh ok. So will that be a file that can simply be burnt right away? I thought people were already putting these onto Blu Rays to playback?

Exactly. I am personally very attached to shiny disc media, so I burned the MKV to Blu-ray (demux/remux). But the resulting disc has no menu, no extras, and I had to supply my own BD-SUP formatted subtitles (shameless plug). Which for some people might be quite enough, but there might just be one or two obsessive completists in these forums ;)