What type of cloud formation are these dark low-hanging clouds?
Based on your video, it does appear to be a non-rotating wall cloud - but admittedly, it is hard to definitively determine, mainly as it is hard to see any updraft.  

Another example of a non rotating wall cloud is from NOAA's Cloud Classification and Characteristics page (image below):



and their description:


  The lowering denotes a storm's updraft where rapidly rising air causes lower pressure just below the main updraft, which enhances condensation and cloud formation just under the primary cloud base. Wall clouds take on many shapes and sizes. Some exhibit strong upward motion and cyclonic rotation, leading to tornado formation, while others do not rotate and essentially are harmless.


Alternatively and given the possible absence of the characteristic updraft of a wall cloud, it could be a scud cloud, similar to the one shown below



Image source

A scud cloud is defined by Accuweather as being:


  ow, ragged and wind-torn cloud fragments, usually not attached to the thunderstorm base. They are often seen in association with, and behind, gust fronts.
  Scud clouds DO NOT produce severe weather. Scud clouds are often mistaken for wall clouds and tornadoes, especially when attached to the thunderstorm base.


A handy tip to tell the difference between a wall cloud and a scud cloud is (according to Accuweather):


  to watch their relative position with respect to the rain area: scud
  clouds move away from the rain area while wall clouds maintain the
  same relative distance.


A video tutorial is included in the Accuweather site