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Comment by jsjohnst | Hacker News Reader

I don’t see how this can be used to “authenticate” a video. If I’m already editing the video anyway, could you filter the original hum out and replace it with the correct frequency for the time you wanted to fake? There’s got to be a margin of error anyway, so would seem very possible to fake unless I’m missing something.

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You could. The point is to disprove the validity of the video. Correct signature is not a proof the video is valid but incorrect one could be proof that it is not.

In practice, most people who manufactured videos before very recently were simply unaware of this possibility. I learned about it many years ago but I still forgot about it and probably would not try to do anything about it if I was manufacturing a video.

i am curious how/where you learned about this years ago if it was not common knowledge until recently?

I learned about it at least a few years ago watching a history of video game speedrunning video (don't remember the specifics from the video or which video it is, sadly). At least 6 years ago, the speedrunning community used the mains hum to prove that a video was spliced together, rather than a continuous stream.

Also, clearly the creator of this page has been recording the mains hum for at least 6 years, so presumably they also knew about it.

Yes, in the same way you could leave fake fingerprints and DNA at a crime scene.

This was used in a court case in the UK where the defence claimed the police had tampered with a recording - editing together separate recordings into a single one to make their case. An academic 'expert' analysed the recording and corroborated the claimed recording times and the accused were found guilty.

Only if you know to do that. Nothing is ever 100%.

You can use it as evidence either way, especially evidence that something is _not_ genuine. It's not proof though.

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