http://isophonics.net/nnls-chroma
Here's chordify: http://ismir2012.ismir.net/event/papers/295_ISMIR_2012.pdf
That conference has great references but unfortunately hasn't been repeated since 2012 http://www.ismir.net/proceedings/index.php
However, this case would be one of the best cases for it, it's a single instrument, and you could make a careful recording out of it