// seems odd to me, conveniently under the nose, how precise is that? //
I imagine Farage was moving about a bit on screen. The black rectangle could have been over his mouth, over his chin, between his eyes.
They have just taken a screen capture at a point it was under his nose.
And this is not how it was broadcast to the public. This was a tv screen in the studio possibly in the background. When the live feed from Farage was boadcast, it would not have had the tash.