I think we need a sticky topic with a Sony
FAQ 
The situation currently is that all mkv files are remuxed to m2ts which the player streams far better over wifi (less stuttering). Unfortunately FFmpeg cannot remux dts properly and produces a silent file so instead it's transcoded to ac3. This will default to 2 channel in the Serviio console settings. Unfortunately it seems that if you select to keep source channel count the dts to ac3 conversion breaks. Both of these problems will hopefully change in future builds of FFmpeg. See here if you would rather have player-native mkv dts support at the expense of smooth wifi streaming (if you're on a wired connection for instance):
viewtopic.php?f=11&t=1547#p7938If it's just a one-off, you can use a tool called
TSMuxer to manually convert the file from mkv to m2ts. This tool can remux the dts stream properly and it will only take a few seconds even for a 4GB file. Then add the m2ts file to your Serviio library.
You can get comprehensive codec and bitrate info on any file by running FFmpeg -i on it from Serviio's lib folder:
viewtopic.php?f=5&t=1123