if you want to get your mkv as an mp4, its very easy. well, assuming your device or what ever it is can support .h264 video stream of course. in the mkv there are two important components. the video streams, the .h264 of course, and the audio streams, whether its a .dts or .acc or .ac3, or even .mp3.
just use a tool like "mkv extract GUI2" to extract the .h264 and the audio stream. chances are your device will not be able to decode the .dts stream, so you will not hear sound. so you need to first use a tool like "popcorn mkv audio converter", this tool take the dts stream out of the mkv file and convert it to an acc or ac3 or mp3 or which ever you choose that your device will support, then it replaces the dts stream in the mkv, then you use the mkv extract to "demux" the .h264 and the .acc or what ever the audio stream popcorn converted it to. then you use another tool called mp4 muxer to mux the .h264 and the audio stream into a single .mp4 file. the .h264 video stream is untouch, preserving its original quality.
if the mkv file doesn't have the .dts stream then you can just mux what ever audio stream it is into the mp4. mp4 doesn't support .dts -> that's digital theater system
you will have to rename the audio and video stream, the .h264 and .acc, as the same file name for it to work properly, like tittle.h264 and tittle.acc.
there are also other files in the mkv like the subtitle, while you will not be able to mux the subtittle together with the .h264 or the .acc into the mp4, but you can rename the subtitle file the same as the mp4 file and it will still work.
goodluck
