I use an action camera to record videos in .WAV format.  But when I drag file into Movie maker (v 2012  16.4.3528.0331) the following happens:

At first, I can see the first frame visible in the browse (?) area and I get a message saying "Movie maker is preparing the file, and I see a progress indicator at the bottom.  But when complete, the image disappears and the box shows an exclamation mark "!" in the single frame.

It used to work, but this problem recently appeared. The help section says something about codecs, following this lead, I did as instructed and got a list up of codecs installed for Windows Media Player (why? Media Player). The list does not include a codec for .WAV.  I don't know what to do next and I cannot see anything helpful.

Don't know if this has any bearing, my machine runs Windows 7 and the pressure to upgrade to Windows 10 is getting aggressive. I may have accepted at some point and then did not complete the action.