In this situation, are you required to indicate your intention to change the traffic lane?

In the video you are driving in the left lane of a two-lane roadway, you pass under a brick flyover, and beyond it your lane ends - lane-change arrows P-9 direct you into the right lane, where other cars are travelling. You are required to signal your intention to change lanes. The answer is: yes.

The Road Traffic Act requires a driver to signal clearly and in good time with the indicator the intention to change direction or lane, and to stop signalling immediately after completing the manoeuvre; when changing lanes, you must also give way to vehicles travelling in the lane you are moving into. The Regulation on road signs and signals states that lane-change arrow P-9 means an order to move into the neighbouring lane shown by the arrow. The order to change lanes does not free you from using the indicator - it is the indicator that tells drivers in the right lane that you are about to move in front of them, and it gives them time to make room.

Legal basis: Art. 22 para. 4 and 5 of the Road Traffic Act (Prawo o ruchu drogowym); § 87 para. 3 of the Regulation on road signs and signals