MacOS – TextMate File Type Association Guide

I found this in Windows help:

To associate a file name extension with a file type:

1. Open Folder Options in Control Panel.
2. Click Start, and then click Control Panel.
3. Double-click Folder Options.
4. On the File Types tab, click New.
5. Type a new or existing file name extension, and then click Advanced.
6. In Associated File Type, select a different file type to associate with the extension.

If you click New and type in rrx, you can associate that with XML document, so you can then use the XML document default programs.

You'll have to associate the MKV extension with a batch file or PowerShell/VB script that in turn performs the file size check and invokes the appropriate application.

Here's how to do it with a batch file:

1. Open regedit, navigate to HKEY_CLASSES_ROOT\.mkv and note the (Default) value. This is the ProgID. Let's assume it's mkvfile.

2. Navigate to HKEY_CLASSES_ROOT\mkvfile\shell\open\command and modify the (Default) value to something like "D:\MKVSizeCheck.bat" "%1".

3. Now create the D:\MKVSizeCheck.bat batch file with the following contents:

   if %~z1 leq 524288000 (
       start "" /max "C:\Program Files\VLC\VLC.exe" "%~1"
   ) else (
       start "" /max "C:\Program Files\PowerDVD\PowerDVD.exe" "%~1"
   )
   

Here's how to do it with VBScript:

1. Same as above.

2. Navigate to HKEY_CLASSES_ROOT\mkvfile\shell\open\command and modify the (Default) value to something like wscript //B "D:\MKVSizeCheck.vbs" "%1".

3. Now create the D:\MKVSizeCheck.vbs file with the following contents:

   set objArgs = WScript.Arguments
   set objShell = WScript.CreateObject("WScript.Shell")
   set objFSO = WScript.CreateObject("Scripting.FileSystemObject")
   if objFSO.GetFile(objArgs.Item(0)).Size <= 524288000 then
       objShell.Run """C:\Program Files\VLC\VLC.exe"" """ & objArgs.Item(0) & """", 3, false
   else
       objShell.Run """C:\Program Files\PowerDVD\PowerDVD.exe"" """ & objArgs.Item(0) & """", 3, false
   end if
   

Note #1: Modify the paths as required obviously. Also the code above sets 500MB (= 524288000 bytes) as the threshold so change that too as per your needs (very large values may be possible only in VBScript though).

Note #2: You can always use a utility like FileTypesMan to do steps 1-2 if you're unsure about manually editing the registry.

Note #3: Using a batch file will cause a console window to flash which might be irritating. Now this can be hidden using something like Hidden Start or VBScript, but why bother when it's better to directly use VBScript in the first place.