Can’t wait until next fall, when Andris Nelsons finally takes over as music director of the Boston Symphony Orchestra? You don’t have to. Nelsons is the subject of new hourlong documentary, humbly titled “Andris Nelsons – Genius on Fire.” Director Astrid Bscher trailed the celebrated conductor for two years to put the DVD together, capturing some behind-the-scenes moments of Nelsons in rehearsal and performance in England and Germany. (Bscher made a similar movie about Klaus Florian Vogt, trailing the German opera star for seven years.) There are also glimpses of Nelsons’ personal life with his family — his wife is Latvian soprano Kristine Opolais — and friends, as well as interviews with Sir Simon Rattle and Daniel Barenboim. The DVD is available now for about $40.