My current 'pet project' is the retrieval, summarisation and navigation of music and audio. The project was started as a seed of this work is was started as a 3rd year project to write the back end of a search by humming system. It was developed further during a doctorate in the IAM group at the University of Southampton. It can now be found in the form of an open source project called Music and Audio Retrieval Tools, or MaART, which is hosted on SourceForge.
MaART is a set of software components used to investigate and implement retrieval / searching of music and audio. This covers content-based and meta-data based solutions, segmentation and content selection (summarisation) of audio and music. First iterations are based on MIDI but digital audio (e.g. MP3 and WAV) extensions are planned. The final goal is to produce an online audio search engine with the usability and effectiveness of Internet search engines for text, such as Google.
Here is a description of some software developed to demonstrate how Open Hypermedia can be applied to audio and other, time based, media. Open Hypermedia, as it applies to music, is looking at ways to put hyperlinks in music - similar to the way you can place hyperlinks in text documents on the Web. It actually goes a bit further than this, but you get the idea. The latest related buzzword / marketing term is probably Web 2.0, where understanding is applied to content to help make more sense of the way documents are related to each other so that navigating around them to find the desired information is easier.