Xjyuk

Inspired by A double-agent with a conundrum. Everything is hypothetical and while the choice of countries are important, they serve no political purpose.

Tension between the US and China is rising. You are a senior officer working for the CIA, in charge of protecting secret technology from the hands of Chinese spies. You also appear in public often, making you the target of many hostile groups.

One day, there appeared a video, showing you conversing and divulging classified information to China's intelligence counterpart. Espionage, if charged, means maximum security prison for life. The problem? That was not you. You believed that the Chinese government hired a body double and faked the video from mainland China to frame you into espionage. You have to prove your innocence before it's too late, because the system will err on the side of guilt except there exist a "smoking gun" evidence.

You scrutinized the video. It started with the title "CIA senior officer at a secret meeting in Denver, August 2nd 2019." The video then cut to a likeness of you, sitting opposite a desk from two other Chinese senior ranking officers. The video seems to be captured by a hidden high quality camera. The faces were blurred in the video, but the voice sounded exactly like yours. The room was white, illuminated by bright florescence light. Besides the desk, chairs, and a clock on the wall, the room was bare. Nothing about the furniture could have told you anything about their origin. Your likeness was able to capture you quite well, copy your very mannerism and accent. He must have watched a lot of your interviews. He even wore everything that you have, down to the wrist watch. You know that everything talked about in the video are true, but the Chinese could have known that already from previous espionage attempts. The metadata was stripped bare, and no one knows who tipped the video in the first place. You also cannot unblur the face to show that it is actually not you.

Suddenly, you had an idea. You went back to your computer and used one last forensics trick...Bingo! The Chinese might tried very hard in hiding anything that revealed the video's actual location, but this showed that the video is recorded in China and not in America! Coupled with the fact that you never left America, you have found the smoking gun for you innocence!

What is your evidence?

I don't think there's anything in the story that shows that the (fictional) Chinese didn't fake this right, but here's a thing that seems like it might be easy to get wrong and possible to detect:

The US uses 60Hz electrity and China uses 50Hz electricity, which will produce different speeds of lighting flicker from those fluorescent lights (a kind of lighting that is consistently very flickery). If the lighting flicker rate matches the video's frame rate, then there will be either no visible artefacts or there will be more or less static variation in brightness across the image as a result. If it mismatches substantially, then successive frames will either vary in overall brightness or vary in spatial brightness variation, depending on the details of the camera. Either way, if we know the video's frame rate then we should be able to tell whether the lighting is powered by 50Hz or 60Hz electricity.

Some caveats:

It is possible to reprocess video to change its frame rate. It is possible to rig up your own electricity generation so as to produce electricity at a frequency different from what the mains gives you.