Dot underscore music files

Sometimes it's not just our music files and music players we are battling hard to keep on top of; sometimes our operating systems introduce new ways to make our music libraries untidy.

An email recently dropped into my inbox:

I’ve created a new library, Audi MMI, and ran it through bliss and all seemed OK. Everything compliant. When I mount the SD Card on the Mac all looks normal and as I would expect.

When mounted in the car I can see all the folders titled using the artist name. Good.

When I go into the artist folder I see each of the folders titled using the album name. Good

When I go into the album folder I see each individual track and that plays and displays artwork as expected. Good.

Now the bad bit.

There is also a list of bad tracks listed before the good tracks prefixed with ._ which will not play. If I select one then it scrolls through that list greying them out as it goes until it reaches the first of the good tracks when it plays and displays artwork as expected.

"Dot-underscore" files are created by OS X and store data about each file. Note they won't be visible in Finder by default because they begin with a dot which means a hidden file.

Here's a really good writeup by a former Apple engineer on how dot underscore and also .DS_Store files work. It might be worth considering the closing statements:

I fully expect lots of people to [...] list tons of times they've deleted companion files and nothing bad happened. That's fine. There are plenty of wires you can remove in the average automobile and nothing "bad" will happen in most driving situations. That doesn't make it smart, supportable, or even necessary. Leave companion files alone - they're not bothering anything. If you have OCD and feel crawly about those files on your disk, you have issues beyond what any OS can address.

... which is all fine and that, but what about cases where these files actually reduce the usability of your applications and devices, such as within the original correspondent's case? How can these files be deleted and problems avoided?

Using the Terminal to ensure hidden files are displayed so these files can be easily deleted doesn't help; there's an additional filter on Finder to ensure these files aren't shown. Furthermore you stand the chance of problems down the line where applications actually depend on these files.

Instead, there's an application that comes with OS X, dot_clean, which can merge dot-underscore music files into their parent files, and remove the old dot-underscore file. This is the best of both worlds - a removed dot-underscore file and no problems from deleting the file. There are some very simple instructions to running dot_clean on this LifeHacker post.

Thanks to TAYLOR149 for the image above.
tags: os x mac filesystems mailbag
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The Music Library Management blog

Dan Gravell

I'm Dan, the founder and programmer of bliss. I write bliss to solve my own problems with my digital music collection.