A Traditional Music Digital Library: my-ipod

This collection represents the status quo in traditional digital library design for music content. When the collection is built:

1. The selected audio files are automatically converted to a format suitable for streaming over the web
2. Metadata embedded in the files (such as ID3 tags) is automatically extracted and made available to form browsing structures, used in full-text indexes for searching, as well as being manipulated and presented to the user, where applicable.
3. Automatically extracted metadata can be override by manually assigned. This can either be done through a desktop application (the Greenstone Librarian Interface, or GLI for short) a graphical user interface that controls all aspects of collection design, or directly through the web browser, on a per-document basis.

A Walkthrough

Taking as a starting point a set of music files identified as worthy of study, the figure below shows the result of browsing the formed digital library collection by title from a web browser. The figure is a useful snapshot in which to orientate ourselves with the main structure and features to the digital library. Functionality that persistently reoccurs is accessible through the header to the page.

This includes:

• help and preferences (top-right);
• a quick-search option (located just below) with links to more sophisticated searching options; and
• pin-pointing where within the site a user is currently located (top-left).

Browsing in the digital library by titles.

The specific content to this location within the site (in this case browsing by title) is shown beneath the main banner. Various groupings of title can be accessed by clicking on the bookshelf icons vertically aligned as the main part of the page: currently C–D is open, with the remaining letters to the alphabet below this, accessed through scrolling.

Interested in the song Candela our curious musicologist clicks on the link for this. This brings up the document view to this song:

The musicologically enriched document view for Candela.

Normally in a digital library the document view brings up a page that is strongly derived from textual metadata. If the document viewed was a text-document, some summary information such as title and author is typically presented, say in tabular form, before the main text is presented. Even in the case of multimedia digital libraries, the view presented is still strongly derived from textual metadata: this time including details such as the length of the video, the TV company that produced it, whether captions are available, and so forth, accompanied with an embedded video player for viewing the content—essentially more textual metadata (in this case the URL to the video content) which in terms of the user-interface is largely divorced from the other elements displayed on the page.

This contrasts sharply with the document view developed in this digital library. Naturally it allows the song to be played (akin to the embedded video player), however this is largely of secondary importance to the other functionality available this is much more closely integrated.

Implementation details

The core part of the interactive elements in the document view were implemented using SVG combined with Javascript. The left- and right-panning interactively available from the self-similarity map was implemented by processing the raw audio stream, made accessible by the Firefox Audio extension API.

AudioDB content based searching was integrated into Greenstone through two components of the digital library software architecture: its build-time document processing plugin system, and its runtime message-passing service-base framework. The developed plugin accepts a wide range of audio formats (including OGG and MP3), and converts them to WAV, the format needed by AudioDB for processing. The new search service took the form of a proxy, accepting messages in the XML syntax used by Greenstone, turning them into the necessary calls to the AudioDB command-line interface, and then converting the output from AudioDB back into the XML syntax expected by the digital library architecture. Finally, the two parts were packaged to operate as a Greenstone extension; the software is available at: http://trac.greenstone.org/gs3-extensions/audioDB/trunk/src.