The controls are frustrating as hell. Every time I miss a jump on that vid, I'm guiding Desmond with what would logically be the appropriate key sequence. III improved on this a lot, at least I didn't have much trouble in the Desmond sequences, but still frustrating without reason.
There are points in this series where the controls can be frustrating, and god knows I suck at playing games, but as far as I can tell in that video the problem was 100% poor judgement. Desmond can't double jump.