Capuçon, Chang, Gringolts, Kremer, Repin, Sitkovetsky, Tetzlaff, Znaider… those are just the violinists who turned up to form part of the Birthday Festival Orchestra for this unique event in 2003. To gather together so many starry names under one roof on the same evening says something for the persuasive powers of festival founder Martin T:son Engstroem whose 50th birthday happily coincided with Verbier’s 10th and Steinway’s 150th – for the accumulation of eight concert grands, all of equal quality, would otherwise surely have been prohibitively expensive without the manufacturer’s largesse.

The film captures the joie de vivre of the occasion as well as music-making that veers from magical to mayhem. I’d view the extra feature first before settling down for the concert itself: between rehearsals, while Andsnes explains that two pianos are more difficult to play than one piano four-hands, the genial Ax admits that ‘with each piano you’re adding twice the trouble, so it becomes exponentially more difficult – 64 times more so than playing two pianos’. You see what he means in the eight-piano/16-hands arrangements. Subtlety and precision are at a premium – I’ve never known a monster piano bash to be any different – but if you can accept the performances as ‘party time for pianists’ then the wince factor is reduced somewhat.

For the most rewarding moments, turn to Argerich and Kissin (fond aunt and talented nephew) playing Mozart’s tricky K521, the slow movement of the Bach concerto, and the rarely heard Smetana Sonata, in a concert that will be most interesting to view 40 years hence.