In the context of the Latin Requiem mass, the words which Mozart set in his Requiem are:
Lacrimosa dies illa
Qua resurget ex favilla
Judicandus homo reus.
Here iudicandus is the simple future passive participle (“going to be judged”), not the passive periphrastic construction. The explanation in the video adds est merely to illustrate how the phrase would look if it were a passive periphrastic (though it isn’t in the original context).