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Shader "Hidden/CameraBlur"
{
    Properties
    {
        _MainTex("Main",2D) = "white" {}
    }
    SubShader
    {
        Pass
        {
            CGPROGRAM
            #pragma vertex vert_img
            #pragma fragment frag
            
            #include "UnityCG.cginc"

            sampler2D _MainTex;
            sampler2D _Tex0;
            sampler2D _Tex1;
            sampler2D _Tex2;

            fixed4 frag (v2f_img i) : SV_Target
            {
                fixed4 col = tex2D(_MainTex, i.uv)*0.25;
                fixed4 col0 = tex2D(_Tex0, i.uv)*0.25;
                fixed4 col1 = tex2D(_Tex1, i.uv)*0.25;
                fixed4 col2 = tex2D(_Tex2, i.uv)*0.25;
                return col + col0 + col1 + col2;
            }
            ENDCG
        }
    }
}

using UnityEngine;

[ExecuteInEditMode]
public class CameraBlur : MonoBehaviour 
{ 
    public string shaderName = "Hidden/CameraBlur";
    Material m_material;
    RenderTexture[] m_rtList;

    void OnRenderImage(RenderTexture src, RenderTexture dst)
    {
        if (m_material == null)
        {
            var shader = Shader.Find(shaderName);
            if(shader == null) return;
            m_material = new Material(shader);
            m_material.hideFlags = HideFlags.DontSave;

            int w = src.width;
            int h = src.height;
            // 1フレームずつずらしたRenderTextureの配列
            m_rtList = new [] {
                new RenderTexture(w, h, 0, RenderTextureFormat.RGB565),
                new RenderTexture(w, h, 0, RenderTextureFormat.RGB565),
                new RenderTexture(w, h, 0, RenderTextureFormat.RGB565)
            };
        }
        // 1フレームずらしたフレームバッファをコピーする
        var tmp = m_rtList[Time.frameCount % 3];
        Graphics.Blit(src, tmp);
        for(int i = 0; i<m_rtList.Length;i++)
        {
            // シェーダにレンダーテクスチャを渡す
            m_material.SetTexture("_Tex" + i, m_rtList[i]);
        }
        // シェーダに渡されたレンダーテクスチャを合成して出力
        Graphics.Blit(src, dst, m_material);
    }
}