Method 1: Installing the Mmcodecchoosermex.dll File to the Windows System Folder 

1. The file you downloaded is a compressed file with the ".zip" extension. In order to install it, first, double-click the ".zip" file and open the file. You will see the file named "Mmcodecchoosermex.dll" in the window that opens up. This is the file you need to install. Drag this file to the desktop with your mouse's left button.

   

2. Copy the "Mmcodecchoosermex.dll" file and paste it into the "C:\Windows\System32" folder.

   

3. If your operating system has a 64 Bit architecture, copy the "Mmcodecchoosermex.dll" file and paste it also into the "C:\Windows\sysWOW64" folder.

   NOTE! On 64 Bit systems, the dll file must be in both the "sysWOW64" folder as well as the "System32" folder. In other words, you must copy the "Mmcodecchoosermex.dll" file into both folders.

   

4. In order to run the Command Line as an administrator, complete the following steps.

   NOTE! In this explanation, we ran the Command Line on Windows 10. If you are using one of the Windows 8.1, Windows 8, Windows 7, Windows Vista or Windows XP operating systems, you can use the same methods to run the Command Line as an administrator. Even though the pictures are taken from Windows 10, the processes are similar.

   1. First, open the Start Menu and before clicking anywhere, type "cmd" but do not press Enter.
   2. When you see the "Command Line" option among the search results, hit the "CTRL" + "SHIFT" + "ENTER" keys on your keyboard.
   3. A window will pop up asking, "Do you want to run this process?". Confirm it by clicking to "Yes" button.

   

5. Paste the command below into the Command Line window that opens and hit the Enter key on your keyboard. This command will delete the Mmcodecchoosermex.dll file's damaged registry (It will not delete the file you pasted into the System32 folder, but will delete the registry in Regedit. The file you pasted in the System32 folder will not be damaged in any way).

   %windir%\System32\regsvr32.exe /u Mmcodecchoosermex.dll

   

6. If you are using a 64 Bit operating system, after doing the commands above, you also need to run the command below. With this command, we will also delete the Mmcodecchoosermex.dll file's damaged registry for 64 Bit (The deleting process will be only for the registries in Regedit. In other words, the dll file you pasted into the SysWoW64 folder will not be damaged at all).

   %windir%\SysWoW64\regsvr32.exe /u Mmcodecchoosermex.dll

   

7. We need to make a new registry for the dll file in place of the one we deleted from the Windows Registry Editor. In order to do this process, copy the command below and after pasting it in the Command Line, press Enter.

   %windir%\System32\regsvr32.exe /i Mmcodecchoosermex.dll

   

8. If the Windows version you use has 64 Bit architecture, after running the command above, you must run the command below. With this command, you will create a clean registry for the problematic registry of the Mmcodecchoosermex.dll file that we deleted.

   %windir%\SysWoW64\regsvr32.exe /i Mmcodecchoosermex.dll

   

9. You may see certain error messages when running the commands from the command line. These errors will not prevent the installation of the Mmcodecchoosermex.dll file. In other words, the installation will finish, but it may give some errors because of certain incompatibilities. After restarting your computer, to see if the installation was successful or not, try running the software that was giving the dll error again. If you continue to get the errors when running the software after the installation, you can try the 2nd Method as an alternative.

Method 2: Copying The Mmcodecchoosermex.dll File Into The Software File Folder 

1. First, you must find the installation folder of the software (the software giving the dll error) you are going to install the dll file to. In order to find this folder, "Right-Click > Properties" on the software's shortcut.

   

2. Open the software file folder by clicking the Open File Location button in the "Properties" window that comes up.

   

3. Copy the Mmcodecchoosermex.dll file into the folder we opened up.

   

4. That's all there is to the installation process. Run the software giving the dll error again. If the dll error is still continuing, completing the 3rd Method may help solve your problem.

Method 3: Uninstalling and Reinstalling the Software that Gives You the Mmcodecchoosermex.dll Error 

1. Push the "Windows" + "R" keys at the same time to open the Run window. Type the command below into the Run window that opens up and hit Enter. This process will open the "Programs and Features" window.

   appwiz.cpl

   

2. The softwares listed in the Programs and Features window that opens up are the softwares installed on your computer. Find the software that gives you the dll error and run the "Right-Click > Uninstall" command on this software.

   

3. Following the instructions that come up, uninstall the software from your computer and restart your computer.

   

4. 4. After restarting your computer, reinstall the software that was giving you the error.
5. You can solve the error you are expericing with this method. If the dll error is continuing in spite of the solution methods you are using, the source of the problem is the Windows operating system. In order to solve dll errors in Windows you will need to complete the 4th Method and the 5th Method in the list.

Method 4: Solving the Mmcodecchoosermex.dll error with the Windows System File Checker 

1. In order to run the Command Line as an administrator, complete the following steps.

   NOTE! In this explanation, we ran the Command Line on Windows 10. If you are using one of the Windows 8.1, Windows 8, Windows 7, Windows Vista or Windows XP operating systems, you can use the same methods to run the Command Line as an administrator. Even though the pictures are taken from Windows 10, the processes are similar.

   1. First, open the Start Menu and before clicking anywhere, type "cmd" but do not press Enter.
   2. When you see the "Command Line" option among the search results, hit the "CTRL" + "SHIFT" + "ENTER" keys on your keyboard.
   3. A window will pop up asking, "Do you want to run this process?". Confirm it by clicking to "Yes" button.

   

2. After typing the command below into the Command Line, push Enter.

   sfc /scannow

   

3. Depending on your computer's performance and the amount of errors on your system, this process can take some time. You can see the progress on the Command Line. Wait for this process to end. After the scan and repair processes are finished, try running the software giving you errors again.

Method 5: Solving the Mmcodecchoosermex.dll Error by Updating Windows 

Most of the time, softwares have been programmed to use the most recent dll files. If your operating system is not updated, these files cannot be provided and dll errors appear. So, we will try to solve the dll errors by updating the operating system.

Since the methods to update Windows versions are different from each other, we found it appropriate to prepare a separate article for each Windows version. You can get our update article that relates to your operating system version by using the links below.

Guides to Manually Update the Windows Operating System 

1. Guide to Manually Update Windows 10
2. Guide to Manually Update Windows 8.1 and Windows 8
3. Guide to Manually Update Windows 7 and Windows Vista
4. Guide to Manually Update Windows XP