AVCHD (.MTS) file import into macOS Photos
In case I can help others with this issues, I'm reposting the "AVCHD (.MTS) file import into macOS Photos" thread from a couple of years ago. After struggling with this for several hours in order to import archived folders containing Sony AVCHD files (spanning several years and all 10+ years ago) into Photos footage from a restored hard drive, I found the following thread, which quickly resolved my issues:
https://forums.macrumors.com/threads/photos-for-mac-how-import-avchd-video.2098717/
Revealing the "MTS" files is helpful; however, Apple's Photos app still will not import them. After trying the new version of Roxio Toast Titanium, which will batch convert the files (as it did years ago) but wasn't retaining all of the metadata (or at least not on the settings that I was using), I thankfully found the MacRumors thread above. I purchased ClipWrap (now EditReady), and successfully --- and quickly -- used its superb "Rewrap" settings to convert each subfolder of revealed MTS files to MOV files, all of which were easily imported into Photos on my Mac (M1 chip running macOS Monterey).
I merely am reposting here in case I can save someone else hours of struggles. There might be other options; however, there is no direct Apple option works unless the Sony video files are saved in MP4 containers (true for newer models). Using EditReady was by far the best and most efficient one for me, despite paying $79.99.
Mac mini, OS X 10.11