Under the dropdown box "Face Detect", you have selected "channel 1,2,3 ...". If you change that one to (eg) Ch1, you'll be able to "smart play". Multiple channels cannot be analysed at the same time.
It doesn't seem to work still. I tried choosing D1 and nothing happens. I wonder why it would say "the behaviour analytics supports one channel only" when I have not selected that option. I've selected Face Detect instead.