Problem with Music Files on USB Drives

elcpu wrote:

I erased the drive using Disk Utility and then copied the mp3s to the drive using Finder. Lo and behold the car then started to "say" that every other file was unplayable. I tried the stick on a music system at home, same issue, every other file unplayable. I then tried a different USB drive, same issue. Long story but the problem is that macOS places a duplicate named copy of every file in the USB drive with the prefix ._ and the extension .mp3 (even though they are not mp3s) and to make matters worse the files are hidden in macOS.

The Finder sees that the external drive does not use a Mac filesystem. It is trying to preserve some extended attributes that a Mac filesystem would maintain, by creating

• FOO.MP3 – the main file
• ._FOO.MP3 – the extended attribute file

The idea being that if you ever copy files back to the Mac, it can transparently combine the data from these two files, to preserve the extended attributes.

macOS is based on Unix, and adding a leading '.' (s a standard Unix convention for hiding a file from regular directory listings. The ._FOO.MP3 name represents an attempt to create a hidden file with a unique name that is easy to associate with the main file.

Unfortunately, other systems don't know about the Finder's "._" games, and may not even know about the Unix convention for hiding a file by starting its name with a "." They see the .MP3 suffix, conclude that the extended attribute files are MP3 files, and of course, then discover that these "MP3" files are hopelessly corrupt.

The same issue happens with preparing thumb drives and memory cards for use with HDTVs and digital picture frames. The ._*.JPG files look like corrupt JPG photos to many third-party devices.

The solution is to go into Terminal just before you eject a memory card or USB flash drive.

1. Go to that volume. (E.g., type cd and a space, then drag-and-drop the memory card or USB flash drive icon.)
2. Do a rm ._*.* to get rid of all files with a leading ._
3. Do a ls -a to identify any remaining files that begin with a .
4. Do a rm on any such files other than . or .. (in Unix, . means the current directory and .. is the parent directory)
5. In the Finder, eject the memory card or flash drive without doing anything else first.

For a MP3 or JPG file, you don't lose all that much by trashing the extended attributes file – even if you do decide to later copy the file back to the Mac.