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 a 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.