::  Posts  ::  RSS  ::  ◂◂RSS  ::  Contact

Audio from Video

August 4th, 2014
tech, ideas  [html]
How does it change the laws around video recording if you can extract some audio information from a video signal?
Researchers at MIT, Microsoft, and Adobe have developed an algorithm that can reconstruct an audio signal by analyzing minute vibrations of objects depicted in video. In one set of experiments, they were able to recover intelligible speech from the vibrations of a potato-chip bag photographed from 15 feet away through soundproof glass. more
Now, this was at 2k-6k frames per second, which is much faster than most cameras, but they were also able to get some data "even from video recorded at a standard 60 frames per second":
even from video recorded at a standard 60 frames per second. While this audio reconstruction wasn't as faithful as it was with the high-speed camera, it may still be good enough to identify the gender of a speaker in a room; the number of speakers; and even, given accurate enough information about the acoustic properties of speakers' voices, their identities.
They briefly mention the Nyquist limit, implying that to reconstruct audio from video you need video frames at twice the frequency of the highest frequency sound you want to record. This would be true if we had only one pixel of data, but we have a whole 2d image. Compare this to looking at waves in a pool. With two timed samples at a point we can tell almost nothing about the wave pattern, but if we take a photograph of the whole pool we can really understand a lot about the waves.

Which then makes me wonder: in many places audio recording must be known to everyone involved but video recording can be secret. Does the technical possibility of audio reconstruction change this? Does this make it illegal to record video of someone without their consent, because a video camera is now just another kind of microphone? Will people in MA have to post signs about their surveillance camera? Or is the illegal act when someone later interprets the video into audio?

Comment via: google plus, facebook

Recent posts on blogs I like:

Cops on Public Transportation

I wrote a post about American moral panics about fare evasion two months ago, which was mirrored on Streetsblog. I made a mistake in that post that I’d like to correct – and yet the correction itself showcases something interesting about why there are arm…

via Pedestrian Observations January 17, 2020

A foolish consistency

“The other terror that scares us from self-trust is our consistency; a reverence for our past act or word, because the eyes of others have no other data for computing our orbit than our past acts, and we are loath to disappoint them. But why should you ke…

via Holly Elmore January 5, 2020

Algorithms interviews: theory vs. practice

When I ask people at trendy big tech companies why algorithms quizzes are mandatory, the most common answer I get is something like "we have so much scale, we can't afford to have someone accidentally write an O(n^2) algorithm and bring the site d…

via Posts on Dan Luu January 5, 2020

more     (via openring)

More Posts:


  ::  Posts  ::  RSS  ::  ◂◂RSS  ::  Contact