Quick answer
Install the K-Lite Codec Pack (basic version) or switch to VLC Media Player, which includes its own codecs. The error means Windows Media Player can't decode the file's audio or video format.
Why you're seeing this error
This tripped me up the first time too. The error NS_E_WMPCORE_SOME_CODECS_MISSING (0XC00D10D1) appears when Windows Media Player encounters a media file that uses a codec not installed on your system. Common triggers include playing an MKV file with H.265 (HEVC) video, or an AVI file using an older DivX codec. It can also pop up after a Windows feature update removes previously installed codec packs (happened a lot with the Windows 10 2004 update). The error is frustrating because WMP doesn't tell you which codec is missing—just that something's wrong.
How to fix it
1. Install K-Lite Codec Pack (the real fix)
Skip Microsoft's own codec packages—they're incomplete and a pain to manage. K-Lite is the gold standard for WMP users. Grab the Basic version from its official website (codecguide.com). During install, choose 'Lots of stuff' preset. This covers H.264, H.265, AAC, MP3, FLAC, and legacy formats like DivX.
After installing, restart WMP and try playing the file again. 9 times out of 10, it works.
2. Use a media player with bundled codecs
If you don't want to mess with codec packs, just switch players. VLC Media Player includes every codec you'll ever need—no separate installs. Download it from videolan.org. Open the file in VLC instead. It handles everything from old WMV files to modern AV1 streams.
You can also try MPC-HC (Media Player Classic Home Cinema), which is lightweight and plays most formats out of the box.
3. Check for Windows Media Feature Pack (Windows N editions)
If you're on a Windows 10/11 N edition, Media Player is crippled by design. Install the Media Feature Pack from Microsoft's website. Without it, many built-in codecs are missing entirely—even for MP4 playback. After installing, reboot and try again.
Alternative fixes (if the main ones fail)
Fix broken codec registry entries
Sometimes codecs are installed but not registered correctly. Open Command Prompt as admin and run:
regsvr32 wmp.dllThen restart WMP. This re-registers Windows Media Player's core codec interfaces.
Disable Windows Media Player's codec download prompt
Go to Tools > Options > Player in WMP. Uncheck 'Download codecs automatically'. This stops WMP from trying (and failing) to fetch missing codecs from a dead Microsoft server. Apply, restart WMP.
Convert the file to a WMP-friendly format
As a last resort, convert the file using HandBrake (free). Choose the 'Fast 1080p30' preset, which outputs MP4 with H.264 video and AAC audio—both supported by WMP natively. It's slower than fixing the codec, but it works.
Prevention tip
Stick with one reliable codec pack—I use K-Lite Codec Pack Basic. Don't install multiple codec packs; they conflict and make things worse. Also, keep your codec pack updated. K-Lite updates every few months to support new formats. Or just use VLC and never think about codecs again.