Adam Resurrected (2008)

Before the war, in Berlin, Adam was an entertainer- cabaret impresario, magician, musician-loved by all until he finds himself in a concentration camp, confronted by Commandant Klein. Adam survives the camp by becoming the Klein's "dog", entertaining him while his wife and daughter are sent off to die. "Adam Resurrected" is the story of a man who once was a dog who meets a dog who once was a boy.

Source: TMDb