Irritating auto-changing column types in Windows Explorer in case of audio/video files

You have to disable the "Automatic Folder Type Discovery" feature present in Windows Vista and later versions. (This solution is tested on Windows Vista, and probably works on Windows 7 as well. I'm not sure about Windows 8 / 8.1 / 10).

Perform the following steps:

Copy-and-paste way:

Copy the following lines into a new text file, save it as "resetfolders.reg" and double-click it:

Windows Registry Editor Version 5.00

; Reset and delete all saved folder customizations and settings.
[-HKEY_CURRENT_USER\Software\Classes\Local Settings\Software\Microsoft\Windows\Shell\BagMRU]
[-HKEY_CURRENT_USER\Software\Classes\Local Settings\Software\Microsoft\Windows\Shell\Bags]

; Turn off Vista auto folder type template discovery. 
[HKEY_CURRENT_USER\Software\Classes\Local Settings\Software\Microsoft\Windows\Shell\Bags\AllFolders\Shell]
"FolderType"="NotSpecified"

; Modify the storage space to 10000 for saving of up to 10000 folder settings.
[HKEY_CURRENT_USER\Software\Classes\Local Settings\Software\Microsoft\Windows\Shell]
"BagMRU Size"=dword:00002710

Long way:

 1. Reset the folder options:

• In Windows Explorer, click Organize -> Folder and Search Options -> View tab -> Folder Options -> Reset Folder
  • The above can also be done by removing the registry keys HKEY_CURRENT_USER\Software\Classes\Local Settings\Software\Microsoft\Windows\Shell\Bags and its subkeys and HKEY_CURRENT_USER\Software\Classes\Local Settings\Software\Microsoft\Windows\Shell\BagMRU and its subkeys.
• go to Folder Options (Organize -> Folder and Search Options) View tab, and make sure the Remember each folder’s view settings is checked.
• Close the Explorer window after changes to save the settings. Windows Vista will only remember the state of folders of the window is closed.

 2. Disable auto discovery:

• Start Regedit, navigate to the key HKEY_CURRENT_USER\Software\Classes\Local Settings\Software\Microsoft\Windows\Shell and perform the following steps:
• Right click on Shell in left pane, select New and then click Key.
• Type Bags to create a key named Bags, and press Enter.
• Right click on Bags that just been created, select New and then click Key.
• Type AllFolders to create a sub-key named AllFolders, and and press Enter.
• Right click on AllFolders that just been created, select New and then click Key.
• Type Shell to create another subkey named Shell, and then press Enter.
• Select Shell key that just been created, and then right click on an empty area in the right pane, click on New and then select String Value.
• Type FolderType as the value name, and press Enter.
• Right click on the Folder Type and click Modify or simply double click on FolderType.
• Type NotSpecified as its value data.
• Click OK.

 3. Increasing the BagMRU Cache Memory Size

• Run Registry Editor (regedit).
• Navigate to the following registry key: HKEY_CURRENT_USER\Software\Classes\Local Settings\Software\Microsoft\Windows\Shell
• If there is not a BagMRU Size value, right click on a blank space in the right pane, then select New, and then click DWORD (32-bit) Value. Then, type BagMRU Size as the value name.
• Double click on BagMRU Size key just created, and then enter 10000 (in decimal base) or 2710 (in hexadecimal base) as its value data.

(source)

1. Go to the highest level folder you have
2. Right-click on the folder and select Properties
3. Select the Customize tab
4. In the top panel select "General Items" from the drop-down
5. Check the box below that say "also apply this template to all subfolders"
6. Click OK

This seemed not to immediately work for me, so I set everything to "Music" which did work and then set everything to "General items" again and that seemed to do the trick.

After the adding the Size column, or making whatever changes you like, save those settings as the default for that kind of folder. You can drag Size towards the left, so that it is easily visible. Then you can either ignore the additional columns or delete them. Then save the resulting layout as default:

First check that you aren't accidentally changing the default for "General Items". Right-click the folder, choose Properties -> Customize. Make sure "Optimize this folder for" is set to Music or Video, as appropriate.

Apply the changes: Organize -> Folder and search options -> View Tab -> Apply to Folders or on Windows 10: View -> Options -> Change folder and search options -> View Tab -> Apply to Folders