https://twitter.com/amagitakayosi/status/928444313880600576

video.frag

precision mediump float;
uniform float time;
uniform vec2 resolution;
uniform sampler2D video1;
uniform sampler2D video2;
uniform sampler2D video3;

vec2 rotate(in vec2 p, in float t) {
    return mat2(
        sin(t), cos(t),
        cos(t), -sin(t)
    ) * p;
}

void main() {
    float t = time * .3;

    vec2 uv = gl_FragCoord.xy / resolution;
    uv -= .5;
    uv.y *= resolution.y / resolution.x;
    // uv *= uv;

    vec2 uv1 = mod(uv * mat2(
      1,  sin(time * .2) * 9.,
      cos(time * .4 + .2) * -.5, 1
    ), .12);
    vec2 uv2 = mod(uv * mat2(
      1, sin(time * .3) * .8,
      cos(time *.3) * 2., 1
    ), .17);
    uv2 = rotate(uv2, t) + .5;

    gl_FragColor = (
        texture2D(video1, uv1) +
        texture2D(video2, uv2)
    ) * .5;
}