I'm working on a project and have recorded a video in movie maker. Then I decided I only wanted to use the audio portion. So again, In movie maker I was able to separate the audio from the video and save to my computer. In trying to import the audiofile into the movie maker project, I'm told that movie maker doesn't support the file (it created!!!). I checked the prompt on how to correct the issue and the suggestion was to play the file in windows media player - said it often corrects any missing codec (?) Then I clicked on the screen, "What kind of files can I use in movie maker?" and looked under Audio to find that it Supports .

Start a new project.
Click the Add videos and photos and add the desired photos or videos (not the one with the audio, but the alternates that you would like to use in place of the original video).
Click the down arrow next to the Record narration button and pick Add sound...
The dialog will open up but initially only with audio files.
Go to the lower right corner and change it from Audio and Music to Videos.
Pick the video file whose audio you'd like to use and click the Open button.

Now you should have whatever photos and video, but with the audio portion from the recorded video.