Neutralizing the iOS camera click sound through active sound cancellation

http://stackoverflow.com/questions/23758875/capture-image-via-capturestillimageasynchronouslyfromconnection-with-no-shutter

by dmd • 12 years ago

334 105 12 years ago

stackoverflow.com

JosephRedfern• 12 years ago

Is this how noise-cancelling headphones work?

citizens• 12 years ago

Not sure, but it's how a lot of karaoke tracks are made.

clay_to_n• 12 years ago

And if an artist releases instrumental or a capella versions of their track, you can usually use this to get the other. Only works if they're exactly the same as the original of course.

robszumski• 12 years ago

That's really interesting. I never knew how they did that. Canceling out the frequencies of the voice makes complete sense.

robin_reala2• 12 years ago

Yes. They have a microphone and a circuit that inverts that input and mixes it into the recording.

mbell3• 12 years ago

That's not really what happens in noise-cancelling headphones. The transforms required are fairly complex, simple mixing is a long way from what is required to achieve good results.

jayd162• 12 years ago

Everyone is getting really excited because they think this is how it works, but no, not exactly.

The shutter sound comes from the same speaker as the anti-shutter sound. The phone is mixing the tracks together and playing nothing.

It's not like both sounds are played and they neutralize each other as sound waves.

lovemenot• 12 years ago

Since it would have more general applicability, I am curious how effective could the noise-cancelling-like method could be? What would be the constraints on its effectiveness?

wyager4• 12 years ago

It's the same process that would happen if you actually played both sounds. The superposition is just happening in software instead of air.

ANTSANTS• 12 years ago

Inverted sound waves can cancel each other in air, I've heard (or not heard) the effect with my own ears.

ertdfgcb• 12 years ago

This is a really cool solution to a problem that really seems like it shouldn't exist.

pliu• 12 years ago

It's all relative. There are probably a lot of subway riding Japanese ladies that would argue that this problem really really should exist.

greggman4• 12 years ago

How do you figure? The same laws don't apply to digital cameras which come on all shapes and sizes.

wyager4• 12 years ago

I'm sorry, but I think if you buy that argument, your priorities are totally out of whack.

Putting legal restraints on someone else's technology because a very small number of people were subjected to mildly embarrassing/uncomfortable situations is ridiculous.

baddox3• 12 years ago

Why? What do you do if you notice someone taking a picture of you? Hearing the sound doesn't solve any problems.

unicornporn• 12 years ago

After all, there must be a reason that there's even A SIGN for it!

http://main.makeuseoflimited.netdna-cdn.com/wp-content/uploa...

cmelbye• 12 years ago

I don't think it's that hard to understand why they might have done it this way, is it? Privacy immediately comes to mind.

_jsn• 12 years ago

The front-facing camera doesn't have an indicator light, so this sound is the only thing preventing an app from stealthily capturing a photo or video recording of you while using it.

I'd imagine analysis of your emotional reaction to some stimuli (gameplay elements, advertisements, whatever) would be fairly valuable.

rrggrr• 12 years ago

Hilarity from the comments: I wish I could upvote twice: once for the inverted-cancelling hack, and once for answering your own question, just to counteract anyone daft enough to downvote you for that. – Daniel Earwicker 1 hour ago

georgiecasey• 12 years ago

i think that was aimed at me. i said in a now deleted comment:

Wow! Even though I know it's allowed, some coolness points deducted for posting the question yourself :-). I'd definitely do the same though. I'd be stopping random people in the street telling them the hack!

i know posting and answering your own questions is encouraged on SO, it was just a joke!

soundoflight• 12 years ago

It looks like he posted it AND answered it at the same time though, which is really weird.

TorKlingberg• 12 years ago

I wonder if Apple is intentionally forcing the shutter sound, to prevent secret upskirt shots. I know several phones have had shutter sounds that cannot be disabled, and some countries have required it. In that case Apple might reject apps that use this trick.

smackfu2• 12 years ago

End user can use the mute switch to turn off the sound. This question is about doing it programmatically.

zbowling• 12 years ago

In Japan, the iPhone will always have the shutter sound even with mute on. You can't disable it or mute it. Even if you didn't buy the phone in Japan, the iPhone will do that in Japan.

Crito• 12 years ago

Isn't the shutter sound, even where required by law, kind of pointless because unsavory users could just take a video instead of taking a picture? That's probably what perverts prefer anyway.

tacotime2• 12 years ago

A true pervert ostensibly might appreciate the additional megapixels offered by a still image over under-sampled auto-compressed video.

phoboslab• 12 years ago

Yes, I believe Apple requires the shutter sound. They actually rejected the first version of my video streaming App because the recording beep was missing.

general_failure• 12 years ago

Shutter sound is required by law in many countries.

stephengillie2• 12 years ago

How do those laws address devices without the capability to produce sound?

baddox3• 12 years ago

Many countries? South Korea is the only one I can find a source for online. In Japan it appears to only be a voluntary choice among device manufacturers.

https://www.privacyinternational.org/reports/south-korea/ii-...

PhasmaFelis• 12 years ago

That was my thinking as well.

I wonder how many of the people cheering this are also the ones horrified by Google Glass because someone might disable the recording light.

pyre• 12 years ago

I don't know about 'cheering' it, but as a hack, it did put a smile on my face.

happyscrappy2• 12 years ago

On Android you can record without the user knowing which is way cooler.

cpach• 12 years ago

Is that really true?

happyscrappy2• 12 years ago

Only if you side load apps and give full permissions.

mschuster91• 12 years ago

How is this possible? Doing ANC would require the sound to be played at the exact same microsecond as the target sound.

mikeash• 12 years ago

I would guess that the sounds are both enqueued, and then playback of both actually starts slightly later, perhaps when the audio hardware indicates that it's ready to start accepting data.

rasz_pl• 12 years ago

VERY low audio latency on iOS. Its not android

colanderman2• 12 years ago

Closer to exact same millisecond. 44.1 kHz sampling rate + 64(ish)-sample buffer granularity = ~1 millisecond.

chronial• 12 years ago

Even that is an overly harsh requirement. While being close does not completely remove the sound but still does severly reduce its volume:

http://www.wolframalpha.com/input/?i=sin%28x%29+-+sin%28x-0....

ja27• 12 years ago

Barely related, but it's surprising how often DSLR newbies show up on photography forums asking how to disable the shutter sound on their cameras.

vpdn• 12 years ago

Awesome hack! If anyone wants try it out and play around, here's a demo project: https://github.com/vpdn/SilentPhotoCaptureDemo

pygy_• 12 years ago

Apple owns the copyright of the shutter sound.

That's enough to reject an app using this trick.

0x0• 12 years ago

I guess the app could read the shutter audio file and invert it on the fly, it doesn't need to ship with the inverted sound upfront. As a bonus it would likely work even if future OS updates changed the sound (well, unless they moved the file so it would no longer be found)

inafewwords• 12 years ago

Another trick is to use a dummy cord. Use a broken headset and cut off the jack. Plug that into the phone.

Diverts sound to headset which doesn't exist. Or just put on a working set of headphones

Neutralizing the iOS camera click sound through active sound cancellation

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