1920x800 is not 16:9, it has had 140 pixels removed from the top and 140 from the bottom
download mkv2vob (
mkv2vob Forums), in the settings change it to output to AVCHD
open the MKV file in it (or drag and drop it), this will then create 2 folders (BDMV and CERTIFICATE)
it will use a little trick to make the file 1920x1080 and if the MKV is already in h264 then it should only take a minute or 2 to complete.
download imgburn, use this to create an iso from the 2 folders
both pieces of software are freeware.
an AVCHD can be burnt to Blu-ray or DVD and it works in exactly the same way except there's no menu's.