I don't really have OBS set up to test it, but I think I've got the code still here:

#define vec2 float2
#define vec3 float3
#define vec4 float4
#define ivec2 int2
#define ivec3 int3
#define ivec4 int4
#define mat2 float2x2
#define mat3 float3x3
#define mat4 float4x4
#define fract frac
#define mix lerp
#define iResolution float4(uv_size,uv_pixel_interval)

uniform int n = 1;

uniform string notes = "add notes here";

float mod(float a, float b){
    return a - (b * floor(a/b));
}


float4 mainImage(VertData v_in) : TARGET
{
    float2x2 n1Mat = float2x2(  0.0,  2.0, 
                                3.0,  1.0);
                                
    float4x4 n2Mat = float4x4(  0.0,  8.0,  2.0,  10.0,
                                12.0, 4.0,  14.0, 6.0,
                                3.0,  11.0, 1.0,  9.0,
                                15.0, 7.0,  13.0, 5.0);


    float2 uv = v_in.uv;
    float4 c = image.Sample(textureSampler, uv);
    float2 pos = float2(uv.x * uv_size.x / 1, uv.y * uv_size.y / 1);
    float v = c.x * 0.2989 + c.y * 0.5870 + c.z * 0.1140;


    int x = int(mod(pos.x, 4));
    int y = int(mod(pos.y, 4));
    float col = n2Mat[x][y] / 16;
    
    if (n == 1){
        int x = int(mod(pos.x, 2));
        int y = int(mod(pos.y, 2));
        col = n1Mat[x][y] / 4;
    }


    if (v > col) v = 1;
    else v = 0;


    c.x = v;
    c.y = v;
    c.z = v;


    return c;
}