Overshadowed (επεσκιασεν). They were up in cloud-land that swept round and over them. See this verb used of Mary (Luke 1:35) and of Peter's shadow (Acts 5:15).

This is (ουτος εστιν). At the baptism (Matthew 3:17) these words were addressed to Jesus. Here the voice out of the bright cloud speaks to them about Jesus.

Hear ye him (ακουετε αυτου). Even when he speaks about his death. A sharp rebuke to Peter for his consolation to Jesus about his death.