Apple Music is erasing my library on external hard drive

.wav files don't carry a tag. If you play such a file directly from Finder, and it is located somewhere within the designated media folder, and Music is set to keep the media folder organized, then Music will add it to the library (so it can play it), use the file name as the song name, and assign it to Unknown Artist, Unknown Album. It will be moved to <Media Folder>[/Music]/Unknown Artist/Unknown Album making it disappear from the folder it was in, but it isn't actually being deleted.

You should use Music > Settings > Files to turn off the Keep... and Copy... options before adding/playing any more .wav files. That way they won't move, and you have a chance to add any metadata that is implied from the file path such as artist or album to the tracks in Music. FWIW the AIFF (.aif) or Apple Lossless (ALAC/.m4a) formats are better containers for lossless audio as they support metadata tags properly. Music can losslessly convert from .wav to one of the others. Apple Lossless makes smaller files with better tagging features, AIFF might be more widely supported outside of Apple's ecosystem.

tt2

How many .wav tracks are we talking about? Once you turn off Keep... & Copy... it should be safe to use File > Import to import the tracks in the media folder without renaming them. Assuming the tracks are in a standard <Artist>/<Album>/[D-]## <Name>.<Ext> layout then it should be possible to write a script to extract the data from the path. There is an older iTunes one at https://dougscripts.com/itunes/index.php but it doesn't handle disc/track numbers so I might roll my own if you'd be interested.

You want the tracks to have the right metadata before you think about converting them. The general process is given in Convert a song to a different file format with the Apple Music app or iTunes for Windows - Apple Support, although what it actually does is make a new copy in the new format. Again, it might need a script if you want the new copy to replace the old in playlists, inherit ratings, play counts, etc. and have the old file discarded or archived so you don't end up with duplicates.

tt2

Or I could find the one I wrote three years ago and post a link to that: https://samsoft.org.uk/iTunes/tagfromfilename.asp.

tt2

Before you do anything else backup what you have now to a second external drive so that you can always restore your original files should anything else go missing.

Are you certain the files have been deleted an not perhaps moved? If you select one of the songs and press cmd+i to show the song info and look at the File tab does it show the location as being in the cloud, or elsewhere?

tt2

Yeah, you are not going to want to that by hand. Can you confirm that in general tracks are in the standard layout? E.g. <Artist>/<Album>/[D-]## <Name>.<Ext> where [D-] is an optional leading disc number and ## is a two-digit track number. Windows typically limits file and folder names to 40 characters, but you can repair any errors there after the fact. I may not be able to get to this until the weekend, but I've already written a Windows script that does the same job so it shouldn't be too hard to do something similar in AppleScript.

tt2

Does the library have ratings, playlists, play counts, etc. that you want/need to preserve or is that already lost? My script can apply information from the path to the library as long as the tracks are added in a way that doesn't move/rename them. Once they are in Music it can convert to a new format that can preserve metadata. I've no idea if dbPoweramp can make sense of the .wav filepath and turn that into metadata when it converts the files.

tt2