What you propose can be done but the SDK does not offer a clean and simple interface to do it. I will just give you some hints of what you could do:
You will have to do two things:
1. Keep drawing the contents of the item when the tracking is lost :
Use the method ’setDrawsOffTracking() from the class CraftARItem. By doing it , the contents will keep drawing even if the tracking is lost.
2. Modify the item’s pose (translation + rotation) at the ‘trackingLost’ event, so the contents are rendered as if it was full-screen.
The item Rotation and Translation specify the position where the Marker was found in the frame. You should have to emulate the parameters that make it look like it’s full-screen. To have an idea of what values you should use, you could use the methods CraftARItemAR.getItemRotation() and CraftARItemAR.getItemTranslation() . Place the marker in a position that makes the video show in full-screen, and write down the values of the rotation and translation at that moment. Then, you can re-use those values at the trackingLost() event, so the video will be rendered with that pose.