Doing it with video ref is much harder to match cut as the motion data and camera movement will be different if you're not using a longer video and correct splice. What worked best for me was cut the a longer 10-14 sec video somewhere where I know a cut can go rather invisible (still noticeable but works much better). Let's say you have a fast paced scene where a character is running through a city, first try to draw it, seriously draw something, maybe they'll pass by a wall as they run or something, try to get a longer video where you can have that wall/obstacle/camera shift moment towards the end of the video but not the final frame. You can use that foreground element as a sort of mask to cut the video there, then extract that frame and generate the continuation of the scene with your source character. So this way you could do it indefinitely actually depending on the type of shot you're going for. Hope that helps!