Not to be picky, but the engine in that video does not use an air starter. It starts with air acting directly on the pistons, fed by an air distributor which times the opening of the air valve in the head of each cylinder. (on big diesels like this each cylinder has its own head)

Only the last part of the video shows the start - the earlier sections of the video are from the "slow turn" part of the start sequence - you can hear air fed to the engine to turn it over slowly to check for any possible hydraulic (water in cylinders) lock.

In the last part of the vid you see the fuel rack go to start position and then the engine turns over and starts. The nominal operating speed for that engine is about 500 rpm. It's a four stroke and still classed as a medium speed engine, not a slow speed engine, which are two strokes.

Rgds,
Chris W.