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hpr1204 :: My Magnatune Downloader

How I download albums from Magnatune with Bash and Perl scripts

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Hosted by Dave Morriss on 2013-03-14 is flagged as Explicit and is released under a CC-BY-SA license.
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Part of the series: Bash Scripting

This is an open series in which Hacker Public Radio Listeners can share their Bash scripting knowledge and experience with the community. General programming topics and Bash commands are explored along with some tutorials for the complete novice.

The Problem

I'm a fan of Magnatune (http://magnatune.com/) and have been buying music from them for 7 or 8 years. The Magnatune website itself is good for exploring and downloading, and interfaces for browsing and purchasing are available in a number of players on Linux. I have direct experience of:

  • Amarok: allows you to browse, purchase, examine artist information and album details.
  • Rhythmbox: the plugin, which used to allow browsing and purchasing, is currently unavailable, but is apparently due to return soon.
  • Gnome Music Player Client: (a front-end to the Music Player Daemon, mpd) offers a Magnatune browser plugin
  • Magnatune Web 2.0 player: a web-based tool which will browse, play and download Magnatune music.
  • Magnatune Android player: a fairly basic browser and player for Android 2.0 and up.

The Magnatune Web 2.0 player is the best of the bunch as far as I am concerned, particularly since it allows me to explore the music collection whilst listening to streamed music at the same time. However, none of these interfaces provide me with exactly what I want in terms of the download process, so I decided to write my own.

The Plan

I currently host my music on my HP Proliant microserver, share it across the home network, and play it with the Music Player Daemon (http://sourceforge.net/projects/musicpd/) on my desktop system. I normally keep the album cover image, artwork and related material in the same directory as the album itself, and I want to be able to save all files in their appropriate places automatically.

Magnatune provides an API which is documented at http://download.magnatune.com/info/api, though this information is only available to members. Data is available in several formats: XML, SQlite and MySQL.

Design

I didn't want to launch into building a full-blown application, especially since I only needed a downloader, so I decided to create a collection of Bash and Perl scripts.

I decided to use the XML data organised by album. This is updated on about a weekly or two weekly basis, and there is a signalling mechanism through a downloadable file containing a checksum. When this changes the large data file has changed and can be downloaded. At the time of writing I simply run this by hand when I receive an email alert from Magnatune.

Magnatune uses an unique key made from the artist and album names which it refers to as the SKU (Stock Keeping Unit) or albumsku. They use this as an URL component and in XML tags. I use it to identify the stuff I download and to keep a simple inventory.

I decided to write some basic scripts:

  • To download the catalogue
  • To extract information from the catalogue
  • To download an album
  • To unpack the downloaded items into the target directory

I wanted to learn more about manipulating XML data, so I decided to use XSL, the Extensible Stylesheet Language. This lets you define stylsheets for XML data, including ways of identifying XML components with XPath and of transforming XML with XSLT.

I have included a number of links to the resources I used in the shownotes.

Repository

I have placed all of the scripts, their associated files, and HTML and PDF README files (extended shownotes) in a GitHub repository. This can be browsed at https://github.com/davmo/magnatune-downloader or, if a copy is required it can be obtained with the command:

  git clone https://github.com/davmo/magnatune-downloader.git

This makes a local git repository containing a copy of all of the files in the current directory.

Note: The code was originally hosted on Gitorious (https://gitorious.org/magnatune-downloader), but with the demise of this service it has been moved to GitHub and the details above have been updated.

Scripts

  • update_albums: a Bash script to download a new version of the album catalogue, as a bzipped XML file, if it is different from the current version. It generates a summary of the catalogue for simple searching using XSLT.
  • report_albumsku: a Bash script to take a SKU code and look up the album details in the XML file.
  • get_album: a Bash script to download an album, cover images and artwork. It takes the SKU as an argument and uses it to make an URL for an XML file which points at all of the components, and this is downloaded (with authentication). The script then parses this file to get the necessary URLs for downloading. I only use the OGG format but it could easily collect any or all formats available from Magnatune. The script records the fact that this particular SKU code has been downloaded so that it isn't collected again in error. All downloaded files are given names beginning with the SKU code and are stored for the installation phase.
  • install_download: a Perl script which unpacks the downloaded zip file to its final destination then adds the cover images and artwork to the same place. I used Perl because it allowed me to query the zip file to determine the name of the directory that was going to be created.

Further Developments

I have added further scripts to this system since I created it. I have one that synchronises the music files from my workstation to the server, and two that give me a simple wish-list or queue functionality.

Since I have a 200GB download limit per month on my broadband contract I try not to download music too often and avoid contention with the rest of the family. My queueing system is used to keep a list of stuff I'd like to buy from Magnatune, and I simply feed the top element from the queue into my download script every week or so.

In the future I expect to be refining all of these scripts and making them less vulnerable to errors. For example, I have found a few cases where Magnatune's XML is not valid and this causes the xsltproc tool to fail. I'd like to be able to recover from such errors more elegantly than I'm doing now.

At some point I may well be tempted to consolidate all of the current functions into a single Perl script.

Disclaimer

I have no connections to Magnatune other than being a contented customer.

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