In this case, the crew has performed a "Single engine taxi" procedure. While pushing back, the engine 1 has been started to pressurize the green hydraulic system. As the engine 2 provides normally the yellow hydraulic system, you could hear the electric pump switched ON at 8:48 in order to get all the hydraulic systems pressurized and the correct flaps/slats moving (The blue elec pump operates once one engine is running or manually). At 12:17, the yellow elec pump is switched OFF and the PTU takes over while the crew starts engine 2.
In this case, the crew has performed a "Single engine taxi" procedure. While pushing back, the engine 1 has been started to pressurize the green hydraulic system. As the engine 2 provides normally the yellow hydraulic system, you could hear the electric pump switched ON at 8:48 in order to get all the hydraulic systems pressurized and the correct flaps/slats moving (The blue elec pump operates once one engine is running or manually). At 12:17, the yellow elec pump is switched OFF and the PTU takes over while the crew starts engine 2.