Alright. I took a gander at the video you linked. Specifically the portion you mentioned in the original post. I have never seen that footage before, and I would say it is likely not "actual" footage. The pictures of the dead could possibly be relevant, along with the black and white hanging photos. The problem is there is no sources for any of it in the video from what I can tell. It could be pictures from the Holocaust for all we know, for example.

I would be dubious of the entire video to be honest. Right after the linked part you posted the narrator went on to say that "Stalin would go on to eliminate 40 million." That number is beyond any reasonable calculation to say the least. It is simply just outside of feasible numbers for Russia, ignoring actual data completely and just looking at it rationally. The Soviet Union had a population of roughly 160 million in 1931, if Stalin went to kill 40 million that would be over a third of the population PLUS then Hitler would invade and estimates from that is another 21-28 million, would mean that almost half the population died during a 20 year period. Yet census data shows that the Soviet Union's population continued to grow, dipping in 1950, but only by 10 million.

To put it into comparison, The Black Book of Communism (one of the most biased books about this subject) put the Stalin death toll at 20 Million. I have posted before saying that more realistic tolls put it under 10 million. Timothy Snyder, author of Bloodlands, estimated Stalin killed around 4 million including those killed during the Holodomor in Ukraine.

Therefore, the video seems to be just a over dramatic retelling of the events of Stalin's terror without any basis in reality. So, honestly, I would take the video and the footage within with a grain of salt unless they can prove that the videos taken were of Great Terror, and if they would look at their ludicrous claims.

Note: I am not denying that the Great Terror happened, or that there was hundred of thousands under the Soviet government during the period of Stalin's rule. I am stating that purposely inflating numbers in order to sensationalize an event is wrong. The numbers presented defy logic. Furthermore, this is not an attempt to say Stalin only killed X number, so he wasn't terrible. One death because of political motives is one death too many. The number the Soviet Union killed was abhorrent and should stand as a testament of what ideology and terror can cause humanity to commit.