When you try to import audio files like AVCHD (MTS), MP3, and MP4 files in your project using Premiere Pro CC, you could get an error message that says, "The file has an unsupported compression type." This error is sometimes noticed with other Adobe audio and video products like After Effects and Media Encoder.
If you still see an issue, change the file directory where the AVCHD files reside and check if the issue gets resolved. For example, if the folder structure is:
Create another folder, XYZ, and move the contents of the AVCHD folder to XYZ folder.
Ensure that the folder structure of the MTS files is identical to the original folder.
Check if you are using a trial version of Adobe Premiere Pro CC. If you are using a trial version, you would experience problems with importing AVCHD and MP4 files as the required .dll files are not installed in the location, C:\Users\Public\Public Documents\AdobeInstalledCodecs. Upgrade to a paid creative cloud membership.