In this situation, as you continue driving, are you obliged to indicate your intention of changing lanes?

In the video you are driving in the right lane of a two-lane roadway in a city; sign F-17 by the road and lane-change arrow P-9 on the roadway tell you that your lane is ending and you have to move into the left lane, where other cars are driving. As you continue driving, you are obliged to signal your intention to change lanes with your indicator. The answer is: yes.

The Road Traffic Act requires the driver to signal with the indicator, in good time and clearly, the intention to change direction or lane, and to stop signalling immediately after completing the manoeuvre; when changing lanes, you must also exercise particular caution and give way to vehicles travelling in the lane you are moving into. The Regulation on road signs and signals provides that lane-change arrow P-9 means an order to move into the adjacent lane shown by the arrow. The fact that the lane is ending does not free you from signalling - the indicator tells those driving in the left lane that you are about to move in front of them.

Legal basis: Art. 22 para. 1, 4 and 5 of the Road Traffic Act (Prawo o ruchu drogowym); § 87 para. 3 of the Regulation on road signs and signals