NS_E_MMS_NOT_SUPPORTED (0XC00D2EFA) Fix

You're trying to stream an audio or video feed—maybe a radio station, a live security camera, or an old IP camera—and Windows Media Player or a third-party app throws up error 0XC00D2EFA. The message reads: "The MMS protocol is not supported." This usually happens when the server you're connecting to only supports RTSP (Real-Time Streaming Protocol) and your client is stuck trying to use MMS (Microsoft Media Server protocol). Or the server outright disabled MMS because it's ancient and insecure.

What's actually happening here is...

MMS was Microsoft's proprietary streaming protocol from the Windows XP/Media Player 9 era. Around 2010, Microsoft deprecated MMS in favor of RTSP, which is an open standard. Many servers that once served MMS streams have since dropped it. Your Windows Media Player (or any app using the Windows Media Foundation) still tries MMS first unless told otherwise. The server responds with a rejection, and you get this error.

Another scenario: your corporate network or firewall is blocking port 1755 (MMS default) while leaving port 554 (RTSP) open. The app tries MMS, fails, and doesn't fall back gracefully.

The fix is straightforward

You need to force the URL to use RTSP instead of MMS, or strip the protocol entirely so the app auto-negotiates. Here's the step-by-step.

1. Check the URL you're using. If it starts with mms://, change it to rtsp://. For example, mms://stream.example.com/live becomes rtsp://stream.example.com/live. If the server only supports HTTP streaming (many do now), try http:// instead.
2. Strip the protocol entirely. Some players accept a bare IP and port, like 192.168.1.100:554. Open the stream URL in a text editor, delete the mms:// prefix, and just use the address and port.
3. Disable the MMS fallback in Windows Media Player. This is the nuclear option. Open WMP, go to Tools > Options > Network. Under Streaming proxy settings, select MMS and click Configure. Set it to Use proxy settings of the browser or No proxy. Then uncheck Use MMS for streaming if that box exists (it's hidden in some versions). Apply and restart WMP.
4. Use a different player. VLC Media Player handles protocol fallback better. Open VLC, press Ctrl+N, paste the original mms:// URL, and click Play. VLC tries RTSP, HTTP, and even UDP. It's a good test to confirm the server is alive.
5. Check Windows Firewall. Open wf.msc (Windows Defender Firewall with Advanced Security). Look for inbound rules that block port 1755 or 554. If you see a block rule for wmplayer.exe on port 1755, delete or disable it. Also verify that outbound rules allow TCP/UDP on both ports.

If it still fails

Then the server genuinely doesn't support MMS, and the RTSP stream might be dead too. Try these:

• Check the server admin or documentation. Some old IP cameras require a firmware update to enable RTSP.
• Use a network analyzer like Wireshark to see what the server actually replies when your client sends an MMS handshake. Look for a TCP reset or an HTTP 405 error. That tells you the server is rejecting the protocol outright.
• If you're streaming from a website, the embed might hardcode the MMS URL. Inspect the page source, find the video element, and replace the src value with an RTSP version.
• On Windows 10/11, the legacy Windows Media Player is often replaced by the modern Media Player app. Try that instead—it uses a newer streaming stack that may already skip MMS.

The core lesson: MMS is dead. Stop using it. Every modern streaming server has moved to RTSP or HTTP-based adaptive streaming. Update your links and your player, and this error disappears.