So, you are using Twonky Media Server to stream content to devices on your network? Then you might have noticed that devices that don't natively play MKV format can't access those files. Well, that's simply because Twonky Media Server isn't transcoding MKV by default and if the player also doesn't know the format then you're stuck. Or almost.
For this tutorial I am using a QNAP NAS TS-412 TurboNAS. By default, it uses Twonky Media Server 6 and for this version you should look at this tutorial.
However, if you happened to have install Twonky Media Server 7 (7.09 at the time I'm writing this), then you need to do things just a bit differently.
ssh (putty) to your media server machine (QNAP NAS in this case)
> cd /share/MD0_DATA/.qpkg/TwonkyMedia/resources/ > vi transcoding.db
you will see there a line for the MP4 format, duplicate it on a new line and change the MP4 to MKV (except for "video/mp4", leave that as it is)
reboot the device
The #video: DLNA Mandatory section should look something like this (Twonky Media Server also allows you to add new formats):
PAL,mpg,video/mpeg,MPEG_PS_PAL,720,576 NTSC,mpg,video/mpeg,MPEG_PS_NTSC,720,480 MPEG,ts,video/vnd.dlna.mpeg-tts,MPEG_TS_HD_NA_MPEG1_L2_ISO CIF15,mp4,video/mp4,AVC_MP4_BL_CIF15_AAC_520 MP4,mp4,video/mp4,AVC_MP4_BL_CIF15_AAC_520 WMV,wmv,video/x-ms-wmv,WMVMED_BASE MKV,mkv,video/mp4,AVC_MP$_BL_CIF15_AAC_520