Surveillance Tricks: Sound retrieval from silent video footage

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Shunka Shunka's picture
Surveillance Tricks: Sound retrieval from silent video footage

A friend of mine who knows I study surveillance technology, culture and law linked me this and was pretty freaked out about it.

Those familiar with the field will recognize this as an expansion on the (now fairly well-known) trick of utilizing a laser bounce from a window or other vibrating stationary membrane. What makes this interesting is that it requires no special equipment at all, does not use a laser which might be picked up by sensors calibrated to alert when they notice coherent light, and that even a (poor) quality audio reconstruction can in theory be retrieved from a cell-phone recording. I was particularly bemused by the use of extrapolation on low frame-rate footage to capture audio frequencies at a significantly higher wavelength than the video frame-rate, which at first would suggest a (demonstrably false) limiter on the technology.

https://www.youtube.com/watch?v=FKXOucXB4a8