MfStub

MfStub is a proxy DLL for mf.dll, the main system DLL for Windows Media Foundation.

MfStub can improve the responsiveness of applications that (poorly) use Media Foundation, including Windows Media Player, by forcing the application to always use normal media sessions, instead of slow, unresponsive, DRM-crippled sessions.

MfStub is designed and only tested to work with Windows Media Player 11 on Windows 7, but it may work with other applications that (mis)use Media Foundation in a similar way.

Refer to the How to Install section for installation instructions.

Background

Media Foundation is the primary media processing framework in Windows. It debuted with Windows Vista and is prominently used by most Microsoft applications provided with Windows, including Windows Media Player, Windows Media Center, and Internet Explorer.

One of the hallmark features of Media Foundation is the lockdown and restriction of DRM-shackled content during media playback. This is achieved through the Protected Media Path, which applications may opt-in to when playing media files.

The Protected Media Path (PMP) can enforce extremely expensive and slow trust-validation procedures, even when playing normal (DRM-free) media. Media playback will not start until the validation completes. This significantly degrades the user's experience, by wasting time and burning their CPU for absolutely zero benefit.

Purpose

MfStub was specifically designed for use with Windows Media Player 11 on Windows 7, where WMP 11's usage of Media Foundation causes significant issues:

• WMP 11 always uses PMP sessions for many media types, including MP3 and WMA, regardless of whether or not the specific file being played is DRM-shackled.
• These PMP sessions enact a trust-validation process that is extremely inefficient and slow. On machines with a large component store, this step may take over 2 minutes to complete, before media playback is allowed to begin.
• WMP 11 initializes a new PMP session every single time a new track is played, repeating the extremely slow trust-validation process over again and significantly delaying playback.

As a result, casually listening to music in WMP 11 can result in a miserable user experience of:

1. Click "Play" on a track.
2. Sit through 2 minutes of silence before playback begins.
3. Playback ends and a new track is chosen.
4. Sit through another 2 minutes of silence before playback begins.
5. Rinse and repeat.

MfStub resolves this issue by forcing WMP 11 to create normal (non-PMP) media sessions instead of PMP sessions. Now, the file you clicked "Play" on will actually starting playing when you click "Play".

DRM

MfStub does not bypass DRM requirements on DRM-shackled media. In fact, MfStub guarantees you will never be able to play DRM-shackled media, because your media player will never be able to create the necessary PMP session for it.

MfStub is only suitable for traditional users that enjoy DRM-free content and possess a normal media library, consisting of ripped CDs, downloads from iTunes, etc.

How to Install

MfStub is a proxy DLL. This means you install it by renaming it to take the original DLL's name and then placing it somewhere where the target application will find it first, before finding the original DLL. You also must rename (or hardlink/symlink) the original DLL to the altered name that the proxy DLL expects. Once installed, all of the original DLL's functions are passed through the proxy to the application using it, except for the functions which need to be manipulated (in this case, PMP session creation).

Don't worry if the amount of text here makes this look complicated. It really isn't.

1. Download

1. Go to the Releases and pick a release, such as the latest.
2. Download the mfstub-all-dlls.zip archive for that release.
3. Extract the mfstub-all-dlls.zip archive.
   Inside, you will find a bunch of different DLLs. Each one is for a specific Windows version and bitness (32 bit vs 64 bit).

2. Pick the correct MfStub DLL

You must pick the DLL that matches 1) your Windows OS version and 2) the bitness of the target application (not OS).

• NT60: for Windows Vista and Server 2008
• NT61: for Windows 7 and Server 2008 R2
• NT63: for Windows 8.1 and Server 2012 R2
• NTBC: for all versions of Bugcrash 10, including Retail, LTSC, Enterprise, IoT, Server 2016, 2019, etc.
• x86: for 32-bit applications (typically found in C:\Program Files (x86)\)
• x64: for 64-bit applications (typically found in C:\Program Files\)

For example, if you use 64-bit Windows Media Player 11 on 64-bit Windows 7, you will choose mfstub_NT61_x64.dll.

Your chosen DLL is the proxy mf.dll. Remember this.

3. Locate the correct system mf.dll

You must find the correct version of the real, system mf.dll that matches your target application's bitness.

• If you have a 64-bit version of Windows:

  • The 64-bit version of mf.dll is located at: C:\Windows\System32\mf.dll
  • The 32-bit version of mf.dll is located at: C:\Windows\SysWOW64\mf.dll (yes, the names seem to be backwards - this is correct)

• If you have a 32-bit version of Windows:

  • The 32-bit version of mf.dll is located at: C:\Windows\System32\mf.dll
  • There is no 64-bit version.

For example, if you use 64-bit Windows Media Player 11 on 64-bit Windows 7, you will need C:\Windows\System32\mf.dll.

Your chosen DLL is the original mf.dll. Remember this.

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Once you have identified the correct proxy DLL and original DLL, you can either install MfStub per-application (recommended) or system-wide.

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4. Install per-application (recommended)

MfStub will only affect the application you install it for. All other programs on your computer will remain unaffected.

1. Locate the program files directory of your target application.
2. Copy/hardlink/symlink the original mf.dll into the application directory.
   Note: Copying works today but might cause unexpected problems for you tomorrow. It is much better to symlink the original mf.dll to its new location instead, using a tool like HardLinkShellExt (see how).
3. Renamed the copied/linked mf.dll to m_.dll.
4. Copy the correct proxy mf.dll into the application directory.
5. Rename the copied MfStub proxy DLL to mf.dll.

You will now have two new DLLs in your application directory.

• m_.dll is the original, real, system mf.dll that the proxy DLL will use.
• mf.dll is the MfStub proxy DLL that the target application will use.

Example process with Windows Media Player 11 (64-bit) on 64-bit Windows 7

1. Windows Media Player 11 (64-bit) is typically installed at C:\Program Files\Windows Media Player
2. Copy/hardlink/symlink C:\Windows\System32\mf.dll to C:\Program Files\Windows Media Player\mf.dll
3. Rename C:\Program Files\Windows Media Player\mf.dll to m_.dll
4. Copy mfstub_NT61_x64.dll to C:\Program Files\Windows Media Player\mfstub_NT61_x64.dll
5. Rename C:\Program Files\Windows Media Player\mfstub_NT61_x64.dll to mf.dll

Completed install:

Now you can launch the target program (e.g. WMP 11) and play some media!

4. Install system-wide (not recommended)

MfStub will affect all applications of the target bitness (32-bit or 64-bit) on your computer.

1. Open the system folder containing the original mf.dll (System32 or SysWOW64).
2. Rename the system mf.dll to m_.dll.
   You will probably be unable to do this, since TrustedInstaller owns the file (and for good reason). Only proceed if you know how to safely manipulate and service this file yourself.
3. Copy the correct MfStub proxy mf.dll into the folder.
4. Rename the MfStub DLL to mf.dll.

This install method is for power users only. Windows updates and servicing events will break this setup and potentially cause significant headaches for you later on.

Config

The first time you run your target application with MfStub installed, it will try to write a mfstub.ini config file next to itself, inside the application directory. This config file contains a few options for controlling the behavior of MfStub. Feel free to modify them as you see fit.

This config file is not critical and can be ignored. MfStub will use default configuration if the mfstub.ini file does not exist.

Troubleshoot mfstub.ini not being created:

• Many application directories are write-protected, so only applications launched with elevated permissions can write to them. This includes most programs installed under Program Files and Program Files (x86), such as Windows Media Player. You will have to launch the application with administrator rights in order for it to create the mfstub.ini file.
• Some applications, including Windows Media Player, do not load Media Foundation (mf.dll and co) until the user requests media playback. If you still do not see mfstub.ini, try playing a media file to make sure that mf.dll gets loaded.

Building

This repo consists of a single Visual Studio 2017 solution that builds all release artifacts.

The solution contains x86 and x64 targets and platform-specific code for several versions of Windows. Each OS-specific MfStub DLL is built using the contemporary VS toolset for that OS and is statically linked with the accompanying MSVC runtime.

• NT60_x86 and NT60_x64 are configured to build with the v90 (VS 2008) toolset.
• NT61_x86 and NT61_x64 are configured to build with the v100 (VS 2010) toolset.
• NT63_x86 and NT63_x64 are configured to build with the v120 (VS 2013) toolset.
• NTBC_x86 and NTBC_x64 are configured to build with the v141 (VS 2017) toolset.

If you have all the appropriate VS toolsets installed, you can download and easily build the entire solution with a few clicks.

Credits

• MfStub development uses DllProxyCreator by Jacquelin Potier.
• MfStub binaries uses inih by Ben Hoyt.

Licenses

MfStub

Copyright (c) 2026 TiberiumFusion

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inih

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Copyright (c) 2009, Ben Hoyt
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