I have added a .bat file to the context menu of .avi files with the following .reg file:
Windows Registry Editor Version 5.00
[HKEY_CURRENT_USER\Software\Classes\avi_auto_file\shell\RemuxvideotoMKV]
@="Remux video to MKV"
[HKEY_CURRENT_USER\Software\Classes\avi_auto_file\shell\RemuxvideotoMKV\command]
@="\"C:\\Program Files\\MKVToolNix\\Remux video to MKV.bat\" \"%1\""
It works. I now want the .bat file to start minimized.
I found an answer for almost exactly the same problem here, but I don't understand the syntax, as it refers to a slightly more complex command.