Because most HD video available online are in MKV format this add-in has greater importance. Moreover it also includes a shell extension that provides thumbnail images and detailed file information for MKV video in Windows explorer for an enhanced experience.
The advantage of enabling MKV file support for Windows7, according to Divx, is that it give ability to use hardware acceleration for H.264 video decoding via the system H.264 decoder (where supported). More details and download (via) from Divx.
Windows 7 uses its own DirectShow filters for decoding audio and video formats. Users who likes to use third party filters like ffdshow, CoreAVC, DivX , Cyberlink, etc in Windows 7, there is a freeware tool called Preferred Filter Tweaker for Windows 7, which lets to use third party filters (full details here).