EchoNest has basically taken the web API to a completely new level with their new Remix API.

The API allows not just the analysis of beats and musical characteristics that their basic API offered, it additionally allows coders to modify audio and video files based on the analysis information for programatic remixing.

To get a sense of the amazing results, check out these initial exploratory vids: http://musicmachinery.com/2009/06/21/wheres-the-pow/

More info: http://code.google.com/p/echo-nest-remix/

Does anyone know of any other multimedia API's that allow for the modification of audiovisual assets via API calls?
Any on your wishlist?

Personally, I'd love some good web-based speech to text and face recognition APIs.

(via O'Reilly Radar)