Airliners Cutting Power Right After Takeoff?

This morning I got a great question from Felipe about the apparent power reduction almost immediately after takeoff by many airliners.

A few links:
Blancolirio is a 777 captain with a great YT channel
Mentour Pilot is another airliner pilot with a great channel
And check out the Wikipedia page for Aircraft noise pollution,
as well as the page for the JT8D engine.

This video is generating a lot of comments that are either totally clueless, or are simply restating the completely obvious. Such comments will be discarded at my leisure.

Видео Airliners Cutting Power Right After Takeoff? канала AgentJayZ