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Command line tool to detect duplicate songs in OS X/macOS based on their Audio Fingerprints.
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Command line tool to detect duplicate songs in OS X/macOS based on their Audio Fingerprints.

Important Notice

This is a work in progress, but some core functionality has been finished to let people use this tool to help users in finding duplicates in their music libraries. I cannot be held responsible if this tool somehow destroys your music library, sets fire on your computer, or starts a intergalactic war in the Galactic Federation on your behalf. Keep backups!

Eventually, a binary will be made available for people to easily download and install this tool. In the meantime, you will need to build it yourself.

This tool currently only works for OS X and macOS and there's no plans to port it to other platforms. It was written in Swift 3, so the possibility to port it by third parties is open. Let me know if you port it so you can be featured in this page.


If you have a big music library, identifying song duplicates can be hard. Even if you keep your music library properly organized, you can still find some duplicates lingering around. Probably some copy of a song you download years ago with no metadata is still hanging around your iTunes Library. Or you could have amased gigantic amounts of music in the past years, and you didn't care about duplicates at first. But you do now, and cleaning them is not going to be an easy task.

Many tools have appeared in the past years that help you with this task. The problem is none of them (if any) use audio fingerprinting, and they relay on song metadata alone. By using audio fingerprinting against a database, you can have better luck finding true duplicates of your songs, without them being considered equal if they are remixes or other variations. If you have ever used iTunes "Show Duplicates" feature, you know the results are never too accurate.

How it works

fsduplicates works by locally generating a fingerprint and sending it off to AcoustID's database to properly identify it and then it returns an AcoustID value that is unique for each song. fsduplicates will search for all the songs recursively inside a user-given directory, send them off to AcoustID, and then save the AcoustID values along with the songs that matched that value in a file within a user-specified directory. This way you can easily see which songs are duplicates of each other.

Getting Started

Before you start using this tool, you should take proper precautions. The current version of this tool (v.0.0.1) will not touch your existing computer files at all. It will however create new files inside directories you specify. Make backups if you want to, and then keep reading.

Installation Guide

fsduplicates was designed to not rely on dependencies, but due to the nature of the project, you will need to install one.

Installing Chromaprint

Chromaprint is a core component of the AcoustID project. Chromaprint includes a command line tool called fpcalc which fsduplicates uses a lot. You can follow the instructions here to install it, or, if you have Homebrew installed on your Mac, you can install it easily using the following command in your Terminal:

brew install chromaprint

Installing fsduplicates

Warning I repeat, this software is incomplete. Use it under your own risk.

Download fsduplicates. Open Finder and select Go > Go To Folder.... Navigate to the /usr/local/bin directory and move the binary there.

If you have Terminal window open, you may need to close it and open it again.

Usage Guide

fsduplicates' commands were designed to be as simple as possible. Typing fsduplicates -h will give you the help info, which you can use to get started:

fsduplicates ver. 0.0.1

usage: fsduplicates [OPTIONS]


 -i                                  When specified for supported commands, makes interaction interactive.
 -f DIR_TO_SEARCH DIR_TO_OUTPUT      Find duplicates in DIR_TO_SEARCH recursively. Output to DIR_TO_OUTPUT
 -fpcalc-path FPCALC_PATH            fpcalc executable path. Default is /usr/local/bin/fpcalc
 -v                                  Verbose mode.
 -s [-i] DIR_TO_OUTPUT               Show all the duplicates for the specified library (DIR_TO_OUTPUT)

Of course this is an Alpha release, so some functionality is incomplete at the time of this writing. The -i and -s are currently not working.

fsduplicates Concepts and Files

It's good to know some concepts I have defined in the development of fsduplicates to use it more effectively.

Whenever you see a command that takes a DIR_TO_OUTPUT parameter, this parameter is called a Library Path. When you are executing operations with fsduplicates, it will generate files and put them in this Library. You need to manually create this Library, either using finder or the Shell's mkdir dir, and pass it on to fsduplicates flags that need it.

The process of going through your music library and getting their AcoustIDs is called Indexing. The indexing process will not move or delete any of your files. It will simply generate new text files with their data.

Depending on the commands, fsduplicates will generate some files inside the Library you passed it.

  • library: This is a plain text file that has all the files it has indexed in a folder you passed as a DIR_TO_SEARCH parameter. For example, it can list all the songs it has proceeded in your Music folder in your Mac User Directory. This file helps fsduplicates avoid reindexing songs and make it more efficient.
  • fps_library: Contains a list of song files and the AcoustIDs returned by AcoustID. Each line has this format: ACOUSTID:SONG_PATH. For discovering duplicates, you'd use this file.
  • no_fps_library: If AcoustID did not return a an AcoustID for one or more song files, their paths will be stored here. Consider contributing the fingerprints of the files listed here to AcoustID to improve their database.

You can open these files, but you should never edit them manually.

Indexing Songs and Finding Duplicates

You can index your songs with the following command:


For example, if you had music by the band Nightwish in the directory /Volumes/iTunes/Music/Nightwish, and you wanted to index them in a new library ~/Documents/fsduplicates_nightwish, you would execute something like this:

mkdir ~/Documents/fsduplicates_nightwish
fsduplicates -f /Volumes/iTunes/Music/Nightwish ~/Documents/fsduplicates_nightwish

Please note that the indexing process can take a very long time if the folder you want to index contains many songs or if you have a slow internet connection. fsduplicates needs to contact AcoustID's database for every song and return the results. And not only that, but AcoustID's rules force developers to not make more than three requests per second. For this reason fsduplicate calls sleep(3) which makes it wait 3 seconds for every 3 requests. Why three seconds instead of one? I do not want the app to appear like a crawler or like a spammy app in general, so I added a longer waiting time. On the plus side, you can start an indexing process and stop it before it completes. Next time you start the scanning process in the same Library, it will skip the files that have already been indexed, saving you some time.

You can try to calculate how long till an scanning operation completes. For example, if a folder contains 180 songs, it would take at least one minute for fsduplicates to finish indexing them. This is a rough estimate, because fpcalc doesn't return immediately either, and it can take a few seconds to finish, depending on the song length.

Working with Duplicates

Automatic Analysis

You can execute the following command to show a list of fingerprint groups containing the songs that match the same AcoustID:

fsduplicates -s LIBRARY

Note that in order to execute this command, you must have executed the indexing process first.


fsduplicates -s ~/Documents/fsduplicates_nightwish

The groups will be sorted by the most amount of duplicates to the least. Sample output:

Showing Duplicates for 08fcc296-7d3f-483f-86ea-cfbe725d291d:
1. /Volumes/iTunes/Music/Nightwish/Bless The Child/02 The Wayfarer.m4a
2. /Volumes/iTunes/Music/Nightwish/Century Child/12 The Wayfarer.m4a
3. /Volumes/iTunes/Music/Nightwish/Ever Dream/03 The Wayfarer.m4a
4. /Volumes/iTunes/Music/Nightwish/Highest Hopes/2-01 The Wayfarer.m4a
5. /Volumes/iTunes/Music/Nightwish/Tales From The Elvenpath/15 Wayfarer.m4a
6. /Volumes/iTunes/Music/Nightwish/Wishsides/2-03 The Wayfarer.m4a

Showing Duplicates for e9ffe05f-ad4a-4906-afca-26cbbf628787:
1. /Volumes/iTunes/Music/Nightwish/Bless The Child/09 Lagoon.m4a
2. /Volumes/iTunes/Music/Nightwish/Century Child/11 Lagoon.m4a
3. /Volumes/iTunes/Music/Nightwish/Highest Hopes/2-08 Lagoon.m4a
4. /Volumes/iTunes/Music/Nightwish/Tales From The Elvenpath/14 Lagoon.m4a
5. /Volumes/iTunes/Music/Nightwish/Wishsides/2-07 Lagoon.m4a

You can execute this command with the -i flag. This will show an interactive prompts where you can do some actions. Currently the only supported action is to create symbolic links of all files in the specified Library.

fsduplicates -s -i ~/Documents/fsduplicates_nightwish

You can then easily load all the symbolic links in a player to listen to them and decided what to do with the duplicates.

Showing duplicates for 08fcc296-7d3f-483f-86ea-cfbe725d291d:
1. /Volumes/iTunes/Music/Nightwish/Bless The Child/02 The Wayfarer.m4a
2. /Volumes/iTunes/Music/Nightwish/Century Child/12 The Wayfarer.m4a
3. /Volumes/iTunes/Music/Nightwish/Ever Dream/03 The Wayfarer.m4a
4. /Volumes/iTunes/Music/Nightwish/Highest Hopes/2-01 The Wayfarer.m4a
5. /Volumes/iTunes/Music/Nightwish/Tales From The Elvenpath/15 Wayfarer.m4a
6. /Volumes/iTunes/Music/Nightwish/Wishsides/2-03 The Wayfarer.m4a
What do you want to do?:
(s)ymbolic link all to Library       (i)gnore


Manual Analysis

After the indexing process is done, fsduplicates will create the three files in the Library I talked about earlier. Following the example above, these files would be:

  • ~/Documents/fsduplicates_nightwish/library
  • ~/Documents/fsduplicates_nightwish/fps_library
  • ~/Documents/fsduplicates_nightwish/no_fps_library

Having these files now, we can use some Shell commands to analyze them better. You don't need to install any new command line tools, as OS X/macOS already comes with the tools you need.

cd to the library (in this case, ~/Documents/fsduplicates_nightwish), and execute these commands:

cat fps_library

This is the basic command to open a file and display it in your Terminal in any UNIX system. Here is a sample of its output:

d038b70a-7298-476f-a1d8-0a8dfdc0e831:/Volumes/iTunes/Music/Nightwish/Wishsides/2-08 A Return To The Sea.m4a
5cf10542-7fad-407c-995c-cd4b2ff0f8f0:/Volumes/iTunes/Music/Nightwish/Wishsides/2-09 Swanheart (Live).m4a
eda19d4e-38e4-496f-a107-c1217971d42f:/Volumes/iTunes/Music/Nightwish/Wishsides/2-10 Deep Sient Complete (Live).m4a
e8b0c206-3b72-43e9-a91b-6d4fbbdf8054:/Volumes/iTunes/Music/Nightwish/Wishsides/2-11 Dead Boys Poem (Live).m4a
5cae6bc9-47ff-4b8a-a4d2-8acdf774432d:/Volumes/iTunes/Music/Nightwish/Wishsides/2-12 Crimson Tide Deep Blue Sea (Live).m4a`

This will show you the list of indexed songs with their fingerprints in the order they were indexed. Not very useful on its own, but the cat command is the basis of many things you can do.

The following is a good command you can type to have a better idea of what songs are duplicates:

cat fps_library | cut -d":" -f1 | sort | uniq -c | sort

This command will show you just the AcoustIDs of all the songs it indexed and how many times this show up. This is a sample on my own machine:

   3 dc663a4b-504a-433a-8460-470e14dbea63
   3 dd383e78-9abc-4b8a-b3e1-8c127322b657
   3 e783d332-254c-4e16-ad58-5c5298416b4e
   4 4a8cbe8e-01b9-415f-bf83-168c4efceacf
   4 b2f77e43-ed0d-4a1e-93b0-24cd08b3d9cf
   4 c22d1eb9-66cd-4566-b41d-6e68f79665a0
   4 c280a720-e92b-4ca0-aecf-3a4fe64386f3
   4 caef6e27-dc4b-45ad-9019-f16ab26830dd
   4 d3f69aac-af0a-4295-b419-47ecb61677e3
   5 772cd814-856e-4181-ab46-49d75bd6b080
   5 78718f73-162f-406e-9d87-276fa56998ed
   5 8278b2e9-eb61-48e7-aef0-254e2a59e739
   5 9552ca9a-94ca-41c6-a008-e90006f89b03
   5 d038b70a-7298-476f-a1d8-0a8dfdc0e831
   5 e9ffe05f-ad4a-4906-afca-26cbbf628787
   6 08fcc296-7d3f-483f-86ea-cfbe725d291d
   6 3b2ccbd5-3ed4-498a-bbd1-d915335927f4

Now you can tell that the AcoustID 3b2ccbd5-3ed4-498a-bbd1-d915335927f4 appears on your library 6 times! With this knowledge in hand, you can now cat fps_library again and then ctrl + f to find the songs that share that ID. You can decide what to do with them (delete them? Move them? up to you).


Even if the AcoustIDs are the same, you should take some care and listen to them before deleting them to ensure they really are the same song. Audio Fingerprinting works great and it has a strong mathematical background, but there's still a chance it will bring back inaccurate results. Still, AcoustID is used by many popular apps used by audiophiles, so there's probably little to worry about.

For Developers

If you want to build upon this tool or submit pull requests, clone the git clone the project like you normally would.

You will have to do two additional steps, namely:

  1. Get an AcoustID API key
  2. Add that API key to the project.

To get an AcoustID API key, head over to the AcoustID website and register an application. You will instantly get your API key. Please ensure that any changes you do to this project play by their rules.

To add the API key to the project, open the project file, extend the Meta group, and create a new plist there. Name it client_id.plist. Ensure that navigate to the physical Meta directory when the prompt asks you where to save the file, otherwise Xcode won't be able to find it.

Your client_id.plist should be like this:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "">
<plist version="1.0">

Replace YOUR_API_KEY with the API key you just got from AcoustID. You should be able to build the project now.


  1. Clean the code.
  2. Finish implementing the (m)ove and (d)delete actions. Some code is ready for this. For anyone interested in taking this task, these operations should only move and delete the files in the filesystem, but it should also delete them from the fps_library file.
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