Matthias Mauch (http://matthiasmauch.net) from the Centre for Digital Music at Queen Mary, University of London talks us through a simple example of labelling a song excerpt with chords in Sonic Visualiser.
Chord labelling can be useful for musicological purposes, or as a reference transcription to test automatic chord labelling algorithms. Or just for music-loving fun.
Sonic Visualiser is a Free Software cross-platform audio analysis program from Queen Mary, University of London. See sonicvisualiser.org/ for more information, downloads, etc.