As far as we can tell, this is not independently verified, but is reported to be a video of protesters in Moscow being arrested for marching in support of Ukraine.
The uniforms appear to be legitimate OMON (OMOH In Russian) uniforms, the Russian special police. The street is Tverskaya, which is the main thoroughfare leading to the Kremlin.
According to the YouTube page (translation):
In the center of Moscow civil activists marched with a giant Ukrainian flag. Eight people gathered in Tver and went to the Kremlin to the sounds of the national anthem of Ukraine. “Raise the Empire and restore the Union,” the statement says. Detained Ekaterina Mal′don, Ildar Dadin, Maxim and Mikhail Chekanov Udimov.