From the Encyclopaedia Britannica: The Soviets pioneered the “cold-launch” method, in which the missile is expelled by gas and the rocket engine ignited after the missile clears the silo. This method, essentially the same system used with SLBMs [submarine-launched ballistic missiles], allows silos to be reused after minor repair.
That barrel-like object is, I expect, the unit that generates the gas that expels the rocket.
Wondering if anyone savvier than me can breakdown this video. Some things I notice:
A 2-stage launch process: 1 to get out of the silo, a 2nd "main stage".
The orange-tinged smoke, mainly in the first stage.
Almost 0 acceleration between the first stage and main stage. (A bit nerve wracking!)
We see some barrel-like metal object get shot out from the side at the start of the main stage.
We also see multiple sealing (?) rings disengage from the fuselage in the start of the main stage.
That barrel-like object is, I expect, the unit that generates the gas that expels the rocket.