NS_E_HEADER_MISMATCH (0XC00D151F) on Windows Media Server

You'll see this error when Windows Media Services (WMS) is streaming content and a server-side component — like a custom plug-in, a playlist command, or a dynamic content source — tries to apply an operation that expects a different media header than what the current stream actually has. For example, a WMS plug-in that assumes every stream is Windows Media Video but gets handed an MPEG-2 stream from a live encoder. The error code 0XC00D151F (NS_E_HEADER_MISMATCH) means the command doesn't apply to the current media header user by a server component. The exact wording in the logs is: "The command does not apply to the current media header user by a server component."

What's actually happening here

Every media stream served by WMS has a header — metadata that describes the codec, bitrate, resolution, and other properties. When a server component (like a content source, a playlist entry, or a custom C++ plug-in) sends a command — say, "skip to frame 100" or "change bitrate" — that command must match the header's characteristics. If the command was designed for a stream with a different codec or format, Windows Media Server raises this error instead of applying it.

Think of it like trying to send a command meant for a DVD player to a Blu-ray player — the command format doesn't match the device's expected instructions. The header is the player's language, and the command is spoken in a different dialect.

The most common triggers:

• A custom plug-in written for a specific codec (like WMV) but the incoming stream is H.264 or MPEG-2.
• A playlist that mixes different media types without proper header re-negotiation.
• A live source that switches encoding profiles mid-stream (rare, but happens with some encoders).
• An outdated WMS version that doesn't support newer codecs (e.g., Windows Server 2003's WMS 9 won't handle H.264 natively).

The fix — step by step

Skip the obvious stuff like restarting the Windows Media Services service — that's a placebo. The real fix depends on what's sending the mismatched command.

1. Identify the offending component. Open Event Viewer (eventvwr.msc) and look under Windows Media Services logs. The error event will name the component — usually a plug-in or a content source. Note the exact name and version. If it's a third-party plug-in, check the vendor's documentation for codec compatibility.
2. Check the stream's actual header. Use a tool like ffprobe (from FFmpeg) or GraphStudioNext to inspect the incoming stream. Run:
   

   ffprobe -v quiet -show_entries stream=codec_name,codec_type -of default=noprint_wrappers=1 

   Look at the codec_name field. If the plug-in expects WMV2 or WMA but the stream shows h264 or aac, that's the mismatch.
3. Fix the plug-in or content source. If the plug-in is custom code, you'll need to modify it to check the stream header before issuing commands. The API method to read the header is IWMHeaderInfo::GetAttributeByName — call it first, then compare against expected values. If it's a third-party plug-in and incompatible, contact the vendor or switch to a compatible one. If you wrote the plug-in, add a check like this (pseudo-C++):
   

   HRESULT hr = pHeaderInfo->GetAttributeByName(L"codec", &val, &type);
   if (SUCCEEDED(hr) && wcscmp(val, L"WMV3") != 0) {
       return NS_E_HEADER_MISMATCH; // or handle gracefully
   }

4. Reconfigure the playlist. If you're using a WMS playlist (.wsx), ensure all entries use the same codec and header format. You can enforce this by setting restrictMediaTypes attribute on the playlist element to the exact codec name. Example:
   

   <MediaDir path="C:\Media" restrictMediaTypes="WMV3" />

   This tells WMS to only serve files matching the WMV3 codec, avoiding mismatched headers.
5. Update WMS if on an old OS. On Windows Server 2008 R2 and earlier, WMS 9 doesn't support H.264 or AAC. Upgrade to Windows Server 2012 or later, which includes WMS 12 with broader codec support. Or use a transcode proxy (like FFmpeg) to re-encode streams to a compatible format before feeding to WMS.
6. Test the fix. Restart the WMS service (net stop Was"; net start Was) and reproduce the trigger. If you still see the error, go to the next section.

What to check if it still fails

If the error persists, the mismatch isn't about codec type but about header metadata like bitrate or frame rate. Run ffprobe with more detail:

ffprobe -v quiet -show_streams 

Look for fields like avg_frame_rate, bit_rate, width, height. A plug-in that expects 30fps will choke on 29.97fps — WMS is strict about this. Adjust your encoding pipeline to match the plug-in's expectations exactly.

Also check if the error is intermittent. That points to a live encoder that switches profiles mid-stream (e.g., a hardware encoder that drops from 1080p to 720p on low bitrate). Fix the encoder config to use a constant profile. If you can't control the encoder, you'll need to buffer and transcode on the server before handing the stream to WMS.

Finally, if you're using HTTP delivery and see this error on client connections, it could be a mismatched HTTP header — WMS checks the User-Agent and Accept headers against the stream's capabilities. A client claiming to support only WMV3 but requesting an H.264 stream gets this. Use the server's limitClientBandwidth or clientProtocol settings to restrict which clients get which streams.