At the moment you can download the German version of the BBC documentation, e.g. with Mediathekview, from the ZDF Mediathek: 4th Episode, Wonders of Anatomy – Medical Record X – Borderline Cases of Science.
Note: Video and link currently only work from Germany.

Surgeon Gabriel Weston has spent many years studying the functioning of the human body. In the series «Incredible Medicine: Dr Weston’s Casebook» she presents people from all over the world with the most unusual bodies and abilities.

One of them is the unique body control required for overtone singing (from 10:40 min.). In November 2016, a film team from BBC Science Production, Emma Hatherley (production, direction) and Alexis Smith (camera), produced a film at the Institute of Music Medicine at the University Hospital of Freiburg with Prof. Bernhard Richter and Wolfgang Saus.

Live images from the magnetic resonance tomograph show the complex motion sequences in the mouth and throat that are involved in overtone singing. Interviews explain the scientific background of the phenomenon.