how do i make a triangle grid like the one in this vid

[icedc69772482]

https://www.youtube.com/watch?v=eBauPHgRF2c

[Mylenium]

Nothing complicated in there. The grid is clearly just drawn/ constructed and used as a matte. Any responses to the music and the general animated variation can easily be done using a bit of sampleImage() expression code to modify the luminance of the matte based e.g. on a simple Fractal Noise and occasionally other shapes to highlight a specific sub-set of the triangles.

Mylenium

[Rick Gerard]

I don't know of any standard plugins that will generate a triangular pattern but you can create one with a Shape layer and a couple of repeaters and then add some masking. The random color changes can also be achieved, but it is a bit of a pain.

If you carefully study the screenshot you will see everything that I modified on the shape layer. 

I'm pretty sure there are 3rd party plug-ins or scripts that will generate this kind of pattern.

You could also set up some expressions to automatically position a shape layer triangle and randomize the colors so you could use them as a track matte. It would take me more time than I have to write that expression tonight but it would involve using sourceRectAtTime(), outer radius, position, and scale properties to position the duplicate shapes.