I want to switch from movie playback to a live signal. How can I achieve this without extra hardware?

DSK based switch to Live: (AJA only)

When using an AJA video device with build in keying capabilities you can switch from movie playback to the AV signal which is connected to the input of the card. If you want to use this feature you have to activate the internal DSK of the AJA device by selecting a DSK based method in the Just Control Configuration window. Back in the just:play UI, you will find the Live Input placeholder in the Video tab of the Library. Just use it like you would use a movie. Use the Inspector to change the values such as fade in/out and duration.

Using the AJA downstream keyer means that the video card synchronizes to the incoming video and not to the reference signal. Therefore any reference signal attached to the "Ref In" will be ignored, so make sure that the incoming video signal is stable. In order to stabilize the signal in advance (i.e. before it is sent to the video card input) you must use a frame synchronizer. Suited frame synchronizers can be found here: http://www.aja.com/products/fs/ 

Because the Live signal is passed through the AJA device, the video signal is NOT visible in Just Control.

Buffered based switch to Live:

With version 2 we added a second method to switch to live, which works with 4K enabled devices from AJA and BMD.

In this case, the incoming signal is captured at the input and send directly to our engine (just:out) where it is handled like a movie. So it can be used as a part of a realtime graphics and it can be seen in Just Control. The signal is delayed for the amount of video buffer defined for the engine in just:connect.