I have almost the same problem with mkv or avi files. I have Sony TV BRAVIA KDL55EX620, Sony blu-ray home theater, WDLive, PS3 and Sony blu-ray player. I have tried to use all these devises with Synology Media Server, so I have next results:
1) KDL55EX620 – video freezes each 2-3 minutes for about 10-20 seconds.
2) PS3 -– video freezes each minute for about 10-20 seconds.
3) Sony blu-ray home theater - video freezes each 1-2 minutes for about 10-20 seconds
4) WDLive - I can start video after the second attempt ( after the first attempt WD loses network connection) and video freezes each 5-10 minutes for about 10-20 seconds
5) Sony blu-ray player does not see any playable files.
So, I would appreciate if someone can help me to resolve this issues with freezing of the streaming.