That is a clip from avery good short film originally done by a French newsreel film company who visted the RAF Free French squadrons 346 and 347 at Elvington airfield, Yorkshire. The British voice on the sound track is Guy or Bernard Jefferson saying "starting port inner... etc." who were founding members of the Yorkshire Air Museum.
It is good footage of the Halifaxes, although if you look at the last few take offs it is not Elvington airfield but some where else, and I think you can see the freight pannier in the area of the bomb bay.