From Music Hack Day
Remixer uses the Web Audio API to allow users to remix songs on the web. The user interface helps the user split the song to different sections and snaps all modifications to the beat in the song. By providing a simple user interface on a web site it can save people a lot of time doing simple music editing. The web app is built for Webkit (Chrome and Safari) and can be found at http://remixer.aranja.is.
This video explains the hack: http://www.youtube.com/watch?v=TaZs0b5e1FE
We are two software developers from Iceland.
Eiríkur Heiðar Nilsson
 About the Hack
We created an web app to remix songs. It is for people that are interested in mixing together a few song quickly or just make a shorter version of one song. To make the app simple to use, we gather information about the songs from Echonest and give the user better hints and guidance from that information.
With this hack you can pick a mp3 file in your computer, remix it in the browser and then download an mp3 file of the final mix (with a little assist from the server).
 Technology used
We used the Web Audio API to be able to work with songs in the browser without needing to upload it to the server. We only sent the file to the server to get metadata from echonest, but were able to start working with the song without uploading it.
This was an experiment for us what we could do with the Web Audio API and we are pleased with the result.
The web app is using Python and Flask on the server, but most of the code is written in CoffeeScript and runs in the browser.