Something is a bit odd in this video. I can see it's probably not an alto sax as it seems too small for that but is it really a soprano? It doesn't seem high enough in tone and if the bell was straightened and the neck too was straight then the sax would reach the guys knees which a true sop would not. I am baffled.
When I heard the song on the Radio 2 folk show last night, I was thought he sounded a bit alto-ish, but the range of the instrument seems to fit with a sop - there are also other Youtube clips of him playing a straight instument (which could of course be a saxello). Not the clearest of videos which doesn't help.