If you've ever browsed to a folder full of AVIs in Windows Explorer you would have noticed that it can take a while for the duration column to fill up. This isn't a big problem, but it is annoying when you try to delete some of the AVIs. This is because an explorer plugin is reading and calculating the lengths and often has a lock on the file when you try to delete it.

If you want to fix this then try this:

1. Open up regedit
   
2. Goto HKEY_CLASSES_ROOT\SystemFileAssociations\.avi\shellex\PropertyHandler
   
3. Delete the "Default" value which should be "{87D62D94-71B3-4b9a-9489-5FE6850DC73E}"

Of course this disables the plugin totally for AVI files which means the duration column (and some other columns) will never be populated. Personally I much prefer to be able to delete the files when I want to rather than to know how how long they are.