As I mentioned earlier, and something Charles picked up on too, the clue to locating where these barracks were situated is the utility poles.
To cut to the chase, I believe the building that is burning in the above video is one of the seven barracks in Compounds BIb or BIa that I've outlined in this image:
The building adjacent to the burning building in the video still is indisputably a bog standard pre-fabricated Pferdestallbaracken (horse stable barrack) of which there were over 150 at Birkenau; mainly used as prisoner accommodation, but also used as hospital barracks, washrooms, latrines and even kindergartens for Jewish children. The building next to it, the one which is on fire, is very likely just another of them.
In the entire camp, the only ones that sat with their length (not their breadth, as the majority of them did) parallel to a fence, are those on the southern edge of Section BII, and those on the northern edge of Section BI:
The photographs below were shot from the so-called selection ramp, visible in them are the same types of almost 'A' shaped utility poles that are visible in still of the burning barrack, and again the utility poles are in front of wooden stable barracks. The first photo definitely shows Barrack 6 of Compound BIb, and the second photo almost certainly shows the same building, as it shows the same people.
We can confirm on other photographs that both the utility poles and telegraph poles were on the southern side of the railway tracks in Birkenau. Therefore we can be sure that the burning building was situated in Section BI, as there would not have been another set of utility poles only 300ft away on the southern edge of Section BII running parallel to these ones, that would have been silly.Soviet Footage.
In the Soviet footage of Birkenau shot from the plane which features in the video Charles uploaded and posted on the thread, you can confirm that several of the wooden barracks are still present and correct. You might be able to see more than I can, but I only annotated on the image below the block numbers of the barracks that are incontestably discernible:Which one was it?
I don't know. I also don't believe, on the available evidence, there's anyway of telling whether the barrack was burnt down after the Soviets shot the footage from the plane, or if it had already been destroyed, and in the film released to the public the footage of the ruins has been cropped off.
There is snow on the roof of barrack next to the one that is on fire, although in the Soviet footage the snow has melted from the many of the roofs. But it was Poland in late January/early February, after the Soviets has shot the footage from the plane those roofs might have been covered in a fresh blanket of snow within a few hours.
But to finish, I'll just illustrate one of the possibilities. If
it was Barrack 24 in Compound BIb that was the building on fire in the still, this one...
... then this image obtained from Google Earth shows both the chimneys (possibly reconstructed, it is Auschwitz we're talking about!) and the lamp that is visible in the photographic still: