• Adobe After Effects Expressions

  Random frame on trigger

  Posted by Justin Stephenson on June 12, 2014 at 6:39 pm

  Hello,

  I am working on an animation in which I would like to trigger a random frame in a frame sequence based on an audio event (an irregularly timed click). The frame would hold until the next trigger.

  I can very easily create a boolean switch from the audio using soundkeys or an expression. I am having a more difficult time figuring out how I would use this to trigger a random frame which would hold until the next trigger.

  I would appreciate it if someone could point me in the right direction.

  Best,

  – Justin

  ————————-
  Design, Animation, Editing, Color for Cinema, Broadcast, Web and Installation.

  Gear: 2 X Macpro 8 Core Nehalem, ATTO R380, Proavio EB8MS, nVidia GTX-286, Blackmagic Decklink Studio, AJA LHi, FSI LM-2461W, Tangent Wave, Yamaha HS50Ms W HS10w Sub

  Tools: Avid MC 5.5 (formerly FCP), CS 5.5, C4D13, Resolve 8.1, VDMX, Quartz Composer, Processing, Cubase 5.

  Justin Stephenson replied 11 years, 11 months ago 2 Members · 2 Replies
• 2 Replies

• 

  Dan Ebberts

  June 12, 2014 at 6:56 pm

  I think you first need to count how many triggers there have been up to the current time. This should help with that:

  https://www.motionscript.com/design-guide/audio-count.html

  Then use the resulting value (n) to seed the random number generator:

  seedRandom(n,true);

  Then select the random frame:

  framesToTime(Math.floor(random(number_of_total_frames)))

  Something like that.

  Dan
• 

  Justin Stephenson

  June 12, 2014 at 7:48 pm

  Perfect! Thank-you, Dan. I also used the counter to create random seeds for some fractal noise layers that I am using for textures and light.

  The end effect is that each time the bass drum is hit, a new background appears.

  Best,

  – Justin

  ————————-
  Design, Animation, Editing, Color for Cinema, Broadcast, Web and Installation.

  Gear: 2 X Macpro 8 Core Nehalem, ATTO R380, Proavio EB8MS, nVidia GTX-286, Blackmagic Decklink Studio, AJA LHi, FSI LM-2461W, Tangent Wave, Yamaha HS50Ms W HS10w Sub

  Tools: Avid MC 5.5 (formerly FCP), CS 5.5, C4D13, Resolve 8.1, VDMX, Quartz Composer, Processing, Cubase 5.

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