While editing a new editing course in the Premiere CC latest update (12.1) MANY of the video clips (mov & mp4) are showing up as audio files. Basically instead of premiere recognizing mp4 or mov as video it would appear it is interpreting them as audio only, both in the project window, preview and timeline.

No obvious way to fix this within the new version, but fortunately there is an easy solution. Downgrade to the last stable version of premiere pro cc (pre v 12.1 update) By doing so, premiere works as normal and you can continue editing your projects on the old version of premiere until Adobe fixes the issue. This 3 minute guide to going back to an old version of premiere pro works for any creative cloud application.

It would seem Adobe's most recent round of updates to Premiere, Photoshop & Lightroom may have been released a little bit early.

Hope this helps until Adobe fixes the new bugs in Premiere 2018!