Why, when I am recording and mixing videos from two cameras simultaneously using AVMultiCamPiP app as I guide, the nominalframerates of the videoAssetTracks I am recording do not have a fixed value (e.g. 30) but floats between 20-30 when the active format I am loading on both AVCaptureDevices supports that (e.g. 'vide'/'420v' 1920x1080, { 1- 30 fps},....) and I set min and max frame duration at 30fps (1,30).