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Link Screen Motion to Audio

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Alfie Newson
Link Screen Motion to Audio
on Jan 21, 2020 at 5:42:41 pm

Hello,

I'm relatively new to after effects so there might be a very simple way to do this but I haven't seen anyone post this specific question online yet.

I have a video file of a short film I made, some of the film takes place with animated 'computer screen' where the camera pans and zooms in and out. To make these parts of the film more interesting I want to add essentially a white noise which 'animates' in response to the motion of the screen mp4.

So when the movement of the pan is quick, the volume of the white noise would rise up in tandem, when it is slow, visa versa.

I was wondering if there was a way to extract motion data to turn into key-frames which I could then link to an audio track?

Is there a way to do this, or anything similar, without animating manually?

Cheers


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John Williams
Re: Link Screen Motion to Audio
on Jan 22, 2020 at 10:56:46 am

Hi there. From what you describe, it sounds like you need to use a 'speed' expression.
The speed expression looks at the speed a layer moves at rather that the value it changes from and to.

So if you have a layer that moves you can create an expression link from an effect (ie Amount of Noice on a Noise effect) and add to the end of the expression:

.speed.toFixed(1)

This will look at the speed of the property rather than the value and the (1) at the end will just round the number up to the nearest decimal point.

As the layer moves faster the speed increases and so will the Amount of Noise, then when it decreases in speed the amount of noise will decrease. Of course you can then add *2 to the end of the expression to multiply it by 2 or whatever, if you need it to be more and /2 if you want to divide the value. This method will work on noise but could be even more interesting on other distortion type effects.

Hope that helps;)

John Williams

Soho Editors


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Alfie Newson
Re: Link Screen Motion to Audio
on Jan 28, 2020 at 4:45:40 pm

Thanks for responding John, I think the speed expression would be useful if I was using animated layers inside after effects however all I have is a static mp4.

If you're interested, I found a way around that by using the subtraction blend mode to give an indication of speed.

- (By stacking one clip above and moving it one or two frames forward, I could see how much movement there was by how much colour difference there is per frame.)

- That gets me the average speed in each frame by going b+w and notching up Gaussian blur.

- Now I'm trying to find a way to gather up the colour data to use it for animating the audio.

Cheers,
Alfie


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John Williams
Re: Link Screen Motion to Audio
on Jan 29, 2020 at 10:41:11 am

That sounds like an interesting method.
Depending on the shot, you could also try tracking a point in the moving shot and then also using the speed expression to generate a value.

John Williams

Soho Editors


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