Windows Media Player traditionally doesn't support the .MKV video file container format natively. MKV (Matroska Video) is an open-source container format popular for its flexibility, allowing multiple video, audio, subtitle tracks, and complex chaptering within a single file. While widely used, it isn't one of the standard formats (like MP4 or AVI using specific codecs) that Windows Media Player includes built-in support for without additional components.

You might encounter MKV files downloaded from online sources or created with open-source encoding tools. It's commonly used for storing high-definition videos, multi-language films, or fan-made content. Windows Media Player might recognize the file but encounter an error stating it doesn't understand the codec within the MKV container (like H.264 video or FLAC audio) because its default set of codecs doesn't include MKV compatibility.

While MKV offers significant advantages for enthusiasts, like bundling diverse media streams and supporting high-quality codecs, its native incompatibility with common players like WMP is a major limitation. Installing a third-party media player with broader format support (like VLC Media Player or MPC-HC) is the simplest solution. Alternatively, users can install codec packs, but this can be complex and pose potential system stability risks. Microsoft has improved codec support in Windows over time, so future updates might eventually provide native MKV playback.