This is the Yigdal prayer. In the video, it is sung according to the Yemenite tune, which is less common than the more widespread Ashkeniza tune (with which I am much more familiar.)
Exalted be the Living G-d and praised, He exists - unbounded by time in His existence. He is One - and there is no unity like His Oneness. Inscrutable and infinite is His Oneness. He has no semblance of a body nor is He corporeal; nor has His holiness any comparison. He preceded every being that was created - the First, and nothing preceded His precedence. Behold! He is Master of the universe to every creature; He demonstrates His greatness and His sovereignty. He granted His flow of prophecy to His treasured splendorous people. In Israel none like Moshe arose again - a prophet who perceived His vision clearly. G-d gave His people a Torah of truth, by means of His prophet, the most trusted of His household. G-d will never amend nor exchange His law for any other one, for all eternity. He scrutinizes and knows our hidden most secrets; He perceives a matter's outcome at its inception. He recompenses man with kindness according to his deed; He places evil on the wicked according to his wickedness. By the End of Days He will send our Moshiach, to redeem those longing for His final salvation. G-d will revive the dead in His abundant kindness - Blessed forever is His praised Name.