I have posted this on the bug tracker.
There's a fix, so I am also posting it here:
The current Amahi DLNA (1.0.16) doesn't stream mkv/m2ts files with VC1 video (i.ex: remuxed blu-rays). (tested on WDTV Live and PowerDVD 12).
This problem was fixed in a version after minidlna 1.0.18.
I have replaced /usr/bin/amahi-dlna with minidlna 1.0.24 from the latest static minidlna package from sourceforge.
This fixes the issue and mkv/m2ts files with VC1 video now play fine.
Furthermore, this version adds new features and fixes many bugs since the amahi 1.0.16 version. For example, folder cover art is now displayed fine with version 1.0.24 on the WDTV (didn't work with the amahi-dlna 1.0.16).
I recommend you update this package ASAP.
Thanks.