UIImagePickerController -设置最大的视频持续时间

I am using the following code to allow users to record video using their iPhone camera, and then upload it directly to my server. I would like to put a limit on the length of the video they can record (5 seconds in this example) and it looks like using videoMaximumDuration would be the obvious way of doing that, but it has no effect. I am using the following code to allow users to