presenter (speaker) change detection from a video clip?
You can use the speech recognition function within Adobe Premiere to (kind of) do this.  It will analyze a long piece of video, and attempt to create a text script of the speech within the video.  If you tick "identify speakers" before it begins, it will write "[speaker 1], [speaker 2]" etc each time it identifies a change in speaker.

However, the success rate is not massively high.  Adobe claim about 75%, with high-quality audio, which seems about right, but is too low to make it a generally useful feature for most people.

There's a step by step guide on how to use it here:
http://layersmagazine.com/powering-search-with-audio-metadata-using-premiere-pro.html