How do these scammer video calls work?

When I was on the 6 hour conversation with the Facebook money flip scammer, there was a part I didn’t understand. At one point, he video calls me. I wish I could have recorded that part. The call was a video (no sound, which is key) which appears to show my cousin waving around a passport card.
Now we know the passport card is fake (he sent it earlier in the conversation and the photoshop work is just bad) and that this video is not my cousin. It’s probably ripped from Tiktok or something, hence the no sound thing. But I am guessing they were able to use a filter or something to make it look like she was talking and holding that card.

Does anyone know how they do this?