Does my brother's prayer, which he performed at my home, become invalid because I played audio clips during his prayer, and what does he owe?

It is not permissible to raise one's voice in the presence of a person praying, as this causes them harm and distraction, according to the Prophet, peace and blessings be upon him: "Indeed, the worshipper is privately conversing with his Lord, so let him consider with what he is conversing, and let not some of you raise their voices above others in reciting the Qur'an." Since you did not know that he was praying, there is no sin upon you, for Allah Almighty says: "And there is no blame upon you for that in which you have erred, but [only for] what your hearts intended." As a reminder, if the sounds are musical, it is absolutely forbidden to play them. Your brother's prayer is not invalidated by your playing those sounds.