The selection of icons should
up to the system not individual applications. A movie (audio, image…) file should be opened in different programs depending on the situation, for example, if you want to view it, edit it or launch a generic hex editor – three different applications should be called. No one of those 3 should in any case completely take over the file extension.
Windows has facilities for creating associations, and allows you to specify any number of commands and choose any file icon:
1) Control Panel -> Folder Options -> File Types
2) HKEY_CLASSES_ROOT Registry key
Here is a picture that illustrates different icons:
