video.glsl

// vertex shader
attribute vec4 a_color;
attribute vec4 a_position;
attribute vec2 a_tex_coord;
varying mediump vec2 v_tex_coord;
varying lowp vec4 v_color_mix;
void main() {
  v_color_mix = a_color;
  v_tex_coord = a_tex_coord;
  gl_Position = a_position;
}

// fragment shader
uniform lowp sampler2D u_texture_luma;
uniform lowp sampler2D u_texture_chroma;
uniform lowp vec3 u_ycbcr_matrix[4];
varying mediump vec2 v_tex_coord;
varying lowp vec4 v_color_mix;
void main() {
  lowp vec3 color;
  lowp vec3 ycbcr = vec3(
    texture2D(u_texture_luma, v_tex_coord).r,
    texture2D(u_texture_chroma, v_tex_coord).ba
  );
  color.r = dot(ycbcr, u_ycbcr_matrix[0]);
  color.g = dot(ycbcr, u_ycbcr_matrix[1]);
  color.b = dot(ycbcr, u_ycbcr_matrix[2]);
  color += u_ycbcr_matrix[3];
  gl_FragColor = vec4(color, 1.0) * v_color_mix;
}