The MG-17 is a belt-fed 8mm machine gun that was used on a large number of Luftwaffe aircraft early in World War II. The gun was developed by Rheinmetall through its subsidiary in Solothurn, Switzerland (as a way to evade the Versailles Treaty restrictions on arms development). The basic action is a short recoil system with a rotating locking nut holding the bolt and barrel together. The basic system was adopted by the Austrian and Hungarian armies as an infantry machine gun, but its main use was in an aerial role.
For aircraft use, the MG-17 was equipped with a belt feed mechanism which was easily interchangeable for either left side or right side feeding. It used a pneumatic system of controls to allow remote charging and firing, and was mounted in the wings or cowling of the Bf 109, Bf 110, Fw 190, Junkers Ju 87, Junkers Ju 88, He 111, Do 17/215, Fw 189, and others. Later in the war the 8x57mm round would become insufficient and the Germans would move to 13mm, 15mm, 20mm, and ultimately even 30mm aircraft guns, but the MG-17 had a huge roles in the early years of the war.
Note that the gun in this particular video has been outfitted with a homemade adapter to mount it on a tripod, so that it can be fired without needing a 75 year old airplane as an accessory.