What can I do if I try to import a video or audio file that is not supported in Windows Movie Maker?
Some audio and video file formats are not supported in Windows Movie Maker and cannot be imported. However, if you have a video or audio file that is not supported, you may be able to use a non-Microsoft video editing program to convert the file into a format that Windows Movie Maker supports, and then import the resulting audio or video file into Windows Movie Maker. Some files also require you to install a codec before you can use the files in Windows Movie Maker.
Note: This information provided by Microsoft.