this is not possible.
for an example - take the native iphone camera app. you cannot change the camera once you start with recording...
though is you use AVCaptureSession to record from within the app and you are writing video via AVAssetWriter, this will look feasible but you have to handle whole recording by yourself however, the video stream will crack and resume (to stop stream from one camera and start stream from other) when you will switch cameras so you will not have seamless video recording experience.