thebookofshaders/08/yuv.frag

// Author @patriciogv - 2015
// http://patriciogonzalezvivo.com
#ifdef GL_ES
precision mediump float;
#endif

uniform vec2 u_resolution;
uniform float u_time;

// YUV to RGB matrix
mat3 yuv2rgb = mat3(1.0, 0.0, 1.13983, 
                    1.0, -0.39465, -0.58060, 
                    1.0, 2.03211, 0.0);

// RGB to YUV matrix
mat3 rgb2yuv = mat3(0.2126, 0.7152, 0.0722,
                    -0.09991, -0.33609, 0.43600, 
                    0.615, -0.5586, -0.05639);

void main(){
    vec2 st = gl_FragCoord.xy/u_resolution;
    vec3 color = vec3(0.0);

    // UV values goes from -1 to 1
    // So we need to remap st (0.0 to 1.0) 
    st -= 0.5;  // becomes -0.5 to 0.5
    st *= 2.0;  // becomes -1.0 to 1.0

    // we pass st as the y & z values of 
    // a three dimentional vector to be
    // properly multiply by a 3x3 matrix
    color = yuv2rgb * vec3(0.5, st.x, st.y);

    gl_FragColor = vec4(color,1.0);
}