This video is called Yellow-cheeked crested gibbons in southern Laos.
From Wildlife Extra:
New gibbon species discovered in Indochina
September 2010. Scientists from the German Primate Center (DPZ) in Göttingen have identified a new species of gibbon: the northern buffed-cheeked gibbon, Nomascus annamensis. Researchers were able to identify it through its characteristic vocalizations. An analysis of the frequency and tempo of their calls, along with genetic research, show that this is, in fact, a new species. Crested gibbons, a monogamous species that live in the tree tops of tropical jungles, are among the most endangered primate species in the world. Knowledge of their biology and distribution is of great importance for their [survival].