The majority of the video is an action being performed by members of HIMA in Yerevan, singing a song which has become like an anthem to many. The words were originally written by Pashinyan himself, later put to music by the group Lav Eli. The explanation and translation of the poem can be found on Armenaker's site.
But, make sure to watch the last minute or so. This is a classic song of the Armenian Revolutionary Federation about Armenian fighters - Fedayis- how appropriate, and how ironic, since the ARF is part of the coalition government.
Here is a rough translation of the refrain of the song:

Who are they, hey!, they are the brave ones
Masis as our witness, they are the fearless of the Armenians.
Who are they, Hey!, they are the valiant ones,
Masis as our witness, they are the Fedayis.