The film posted on video website YouTube shows officers punching 23-year-old William Cardenas in the face six times while placing a knee on his neck during an arrest in Hollywood in August.
"There's no denying that the video is disturbing," Mr Bratton said during a news conference.
"But as to whether the actions of the officers were appropriate in light of what they were experiencing and the totality of the circumstances is what the investigation will determine."
Both officers have been removed from their beats and are performing administrative roles, he said.
Cardenas remains in custody for allegedly resisting arrest during the scuffle and for a felony warrant for receiving stolen goods, according to Bratton.
Accusations of police brutality are a sensitive subject in Los Angeles, which erupted in riots in 1992 following the acquittal of officers involved in the video-taped Rodney King beating a year earlier.