元動画のAVAssetから音声データ(Audio track)のみ抽出

let asset = AVURLAsset(url: url)
let track = asset.tracks(withMediaType: .audio)[0]

新しいAVAssetを生成し、そのAudio trackも生成

let newAsset = AVMutableComposition()
guard let audioTrack = newAsset.addMutableTrack(withMediaType: .audio, preferredTrackID: kCMPersistentTrackID_Invalid) else { return }

newAsset(音声のみのAVAsset)に動画から抽出したAudio trackを挿入

do {
      try audioTrack.insertTimeRange(track.timeRange, of: track, at: .zero)
    } catch let error {
        print(error)
    }

AVPlayerで再生

let player = AVPlayer(playerItem: AVPlayerItem(asset: newAsset))
playerLayer.player = player
playerLayer.player?.play()

コード全体

let asset = AVURLAsset(url: url)
let track = asset.tracks(withMediaType: .audio)[0]

let newAsset = AVMutableComposition()
guard let audioTrack = newAsset.addMutableTrack(withMediaType: .audio, preferredTrackID: kCMPersistentTrackID_Invalid) else { return }

do {
      try audioTrack.insertTimeRange(track.timeRange, of: track, at: .zero)
    } catch let error {
        print(error)
    }

let player = AVPlayer(playerItem: AVPlayerItem(asset: newAsset))
playerLayer.player = player
playerLayer.player?.play()

参考にした記事