If you want to make sure that an unsupported codec is your issue, then download VLC (an incredibly versatile open source media player), install it, and restart your system (if it asks you to). Then open your problem video file using VLC. Once it is open, go to Tools>Codec Information and write down what it tells you the codec is. Then, open a file that plays well in Premiere Pro and using VLC, go to Tools>Codec Information and write down that codec as well. If they are two different codecs, then you’ll know that it was the codec from the problem video file that is giving you trouble, and you can purchase that codec online for Premiere. If they are the same codecs, then it must be another thing entirely. If that is the case, reinstalling Premiere might be your best bet. However, there is an amazing website put up by people who have had codec issues with Premiere in the past that has all sorts of good information about where to find free codecs and what software to use to find the codec that an avi or mov is using. Click on the link above to check it out. Hopefully this helps!
