diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..84c048a
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+/build/
diff --git a/CMakeLists.txt b/CMakeLists.txt
new file mode 100644
index 0000000..da78078
--- /dev/null
+++ b/CMakeLists.txt
@@ -0,0 +1,28 @@
+cmake_minimum_required(VERSION 3.18)
+
+project(blocky C CXX)
+
+option(BLOCKY_STATIC OFF)
+
+set(CMAKE_CXX_STANDARD          20)
+set(CMAKE_CXX_STANDARD_REQUIRED ON)
+
+set(BLOCKY_C_FLAGS
+    $<$<OR:$<CXX_COMPILER_ID:Clang>,$<CXX_COMPILER_ID:AppleClang>,$<CXX_COMPILER_ID:GNU>>:
+      -Wall -Werror -pedantic-errors -Wextra -Wconversion -Wsign-conversion>
+    $<$<OR:$<CXX_COMPILER_ID:Clang>,$<CXX_COMPILER_ID:AppleClang>>:
+      -Wno-overloaded-virtual>
+    $<$<CXX_COMPILER_ID:MSVC>:
+    /W4 /WX>
+)
+set(BLOCKY_CXX_FLAGS
+  $<$<OR:$<CXX_COMPILER_ID:Clang>,$<CXX_COMPILER_ID:AppleClang>,$<CXX_COMPILER_ID:GNU>>:
+    -Wall -Werror -pedantic-errors -Wextra -Wconversion -Wsign-conversion>
+  $<$<OR:$<CXX_COMPILER_ID:Clang>,$<CXX_COMPILER_ID:AppleClang>>:
+    -Wno-overloaded-virtual>
+  $<$<CXX_COMPILER_ID:MSVC>:
+    /W4 /WX>
+)
+
+add_subdirectory(thirdparty)
+add_subdirectory(conv)
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..95c2099
--- /dev/null
+++ b/README.md
@@ -0,0 +1,23 @@
+blocky
+====
+
+## CMake command
+
+When you built openh264 on `/home/user/openh264`:
+```
+cmake -DCMAKE_CXX_FLAGS=-isystem\ /home/user/openh264/codec/api\ -L/home/user/openh264 ..
+```
+
+## ffmpeg useful commands
+
+```
+ffmpeg -i in.mp4 -vframes 300 "%d.png"
+```
+
+```
+ffmpeg -r 30 -i "%d.png" -vcodec libx264 -pix_fmt yuv420p out.mp4
+```
+
+```
+ffmpeg -i src.mp4 -t 10s cut.mp4
+```
diff --git a/conv/CMakeLists.txt b/conv/CMakeLists.txt
new file mode 100644
index 0000000..2d2e5fc
--- /dev/null
+++ b/conv/CMakeLists.txt
@@ -0,0 +1,4 @@
+set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${BLKY_CXX_FLAGS} -I ${PROJECT_SOURCE_DIR}")
+
+add_executable(video_bprob video_bprob.cc)
+target_link_libraries(video_bprob PRIVATE args minimp4 openh264)
diff --git a/conv/common.hh b/conv/common.hh
new file mode 100644
index 0000000..d9236ec
--- /dev/null
+++ b/conv/common.hh
@@ -0,0 +1,75 @@
+#pragma once
+
+#include <stdexcept>
+#include <string>
+
+
+inline void Enforce(bool eval, const std::string& msg) {
+  if (!eval) {
+    throw std::runtime_error {msg};
+  }
+}
+
+inline void CopyNal(std::vector<uint8_t>& v, const uint8_t* buf, size_t sz) noexcept {
+  v.resize(sz+4);
+  v[0] = 0;
+  v[1] = 0;
+  v[2] = 0;
+  v[3] = 1;
+  std::memcpy(&v[4], buf, sz);
+}
+
+
+struct Frame {
+  std::vector<uint8_t> Y;
+  std::vector<uint8_t> U;
+  std::vector<uint8_t> V;
+
+  int32_t w, h;
+  int32_t hw, hh;
+
+  Frame() = default;
+  Frame(uint8_t* yuv[3], const SBufferInfo& frame) {
+    w = static_cast<int32_t>(frame.UsrData.sSystemBuffer.iWidth);
+    h = static_cast<int32_t>(frame.UsrData.sSystemBuffer.iHeight);
+    hw = w/2;
+    hh = h/2;
+
+    const auto ystride  = static_cast<int32_t>(frame.UsrData.sSystemBuffer.iStride[0]);
+    const auto uvstride = static_cast<int32_t>(frame.UsrData.sSystemBuffer.iStride[1]);
+
+    Y.resize(w*h);
+    for (int32_t y = 0; y < h; ++y) {
+      const auto src = yuv[0]   + y*ystride;
+      const auto dst = Y.data() + y*w;
+      std::memcpy(dst, src, w);
+    }
+
+    U.resize(hw*hh);
+    V.resize(hw*hh);
+    for (int32_t y = 0; y < hh; ++y) {
+      const auto offset = y*uvstride;
+      const auto srcu = yuv[1]   + y*uvstride;
+      const auto srcv = yuv[2]   + y*uvstride;
+      const auto dstu = U.data() + y*hw;
+      const auto dstv = V.data() + y*hw;
+      std::memcpy(dstu, srcu, hw);
+      std::memcpy(dstv, srcv, hw);
+    }
+  }
+
+  SSourcePicture GetSourcePic() noexcept {
+    SSourcePicture ret;
+    ret.iPicWidth    = w;
+    ret.iPicHeight   = h;
+    ret.iColorFormat = videoFormatI420;
+    ret.iStride[0]   = w;
+    ret.iStride[1]   = hw;
+    ret.iStride[2]   = hw;
+
+    ret.pData[0] = Y.data();
+    ret.pData[1] = U.data();
+    ret.pData[2] = V.data();
+    return ret;
+  }
+};
diff --git a/conv/video_bprob.cc b/conv/video_bprob.cc
new file mode 100644
index 0000000..c99f98d
--- /dev/null
+++ b/conv/video_bprob.cc
@@ -0,0 +1,355 @@
+#include <cmath>
+#include <cstdint>
+#include <cstdlib>
+#include <cstring>
+#include <fstream>
+#include <stdexcept>
+#include <string>
+#include <unordered_map>
+#include <vector>
+
+#include <args.hxx>
+#include <minimp4.h>
+
+#include <codec/api/wels/codec_api.h>
+
+#include "conv/common.hh"
+
+
+namespace param {
+using namespace ::args;
+
+ArgumentParser parser {
+  "converter: video -> block probability matrix"
+};
+HelpFlag help {
+  parser, "help", "display this menu", {'h', "help"},
+};
+
+ValueFlag<int32_t> bw {
+  parser, "128", "width of blocks (px)", {"block-w"}, 128,
+};
+ValueFlag<int32_t> bh {
+  parser, "128", "height of blocks (px)", {"block-h"}, 128,
+};
+ValueFlag<int32_t> utime {
+  parser, "10", "duration of each feature (frame)", {"utime"}, 10,
+};
+
+ValueFlag<int32_t> bmw {
+  parser, "16", "width of blockmatch region (px)", {"bm-w"}, 16,
+};
+ValueFlag<int32_t> bmh {
+  parser, "16", "height of blockmatch region (px)", {"bm-h"}, 16,
+};
+ValueFlag<int32_t> bmsw {
+  parser, "4", "width of blockmatch search region (px)", {"bm-sw"}, 4,
+};
+ValueFlag<int32_t> bmsh {
+  parser, "4", "height of blockmatch search region (px)", {"bm-sh"}, 4,
+};
+
+enum Output {
+  kProb,
+  kLen,
+  kVec,
+  kNull,
+};
+const std::unordered_map<std::string, Output> kOutput = {
+  {"default", kProb},
+  {"prob", kProb},
+  {"len", kLen},
+  {"vec", kVec},
+  {"null", kNull},
+};
+MapFlag<std::string, Output> output {
+  parser, "prob", "output type (len, vec, null)", {"output"}, kOutput,
+};
+
+Positional<std::string> vpath {
+  parser, "path", "video file path",
+};
+
+}  // namespace param
+
+
+struct Frame {
+  std::vector<uint8_t> Y;
+  std::vector<uint8_t> U;
+  std::vector<uint8_t> V;
+
+  int32_t w, h;
+  int32_t hw, hh;
+
+  Frame() = default;
+  Frame(uint8_t* yuv[3], const SBufferInfo& frame);
+};
+
+struct Vec {
+  double x, y;
+};
+
+// utilities
+static void CopyNal(std::vector<uint8_t>&, const uint8_t* buf, size_t sz) noexcept;
+
+
+static Vec BlockMatching(const Frame& cf, const Frame& pf, int32_t bx, int32_t by) {
+  const auto bmw  = args::get(param::bmw);
+  const auto bmh  = args::get(param::bmh);
+  const auto bmsw = args::get(param::bmsw);
+  const auto bmsh = args::get(param::bmsh);
+
+  int32_t min_sx = 0, min_sy = 0;
+  double  min_score = 1e+100;  // INF
+  for (int32_t sy = -bmsh; sy < bmsh; ++sy) {
+    for (int32_t sx = -bmsw; sx < bmsw; ++sx) {
+      double score = 0;
+      for (int32_t y = 0; y < bmw; ++y) {
+        for (int32_t x = 0; x < bmh; ++x) {
+          const auto c_off = (bx+x) + (by+y)*cf.w;
+          const auto p_off = (bx+x+sx) + (by+y+sy)*cf.w;
+          const auto diff  = static_cast<double>(cf.Y[c_off] - pf.Y[p_off]);
+          score += diff*diff;
+        }
+      }
+      if (score < min_score) {
+        min_score = score;
+        min_sx    = sx;
+        min_sy    = sy;
+      }
+    }
+  }
+
+  const auto sxf = static_cast<double>(min_sx) / static_cast<double>(bmsw);
+  const auto syf = static_cast<double>(min_sy) / static_cast<double>(bmsh);
+  return { .x = sxf, .y = syf, };
+}
+
+static double EachBlock(const Frame& cf, const Frame& pf, int32_t bx, int32_t by) {
+  const auto v = BlockMatching(cf, pf, bx, by);
+
+  const auto len = std::sqrt(v.x*v.x + v.y*v.y);
+  switch (args::get(param::output)) {
+  case param::kLen:
+    std::cout << len << '\n';
+    break;
+  case param::kVec:
+    std::cout << bx << " " << by << " " << v.x << " " << v.y << '\n';
+    break;
+  default:
+    break;
+  }
+  return len;
+}
+
+static void EachFrame(const Frame& cf, const Frame& pf) {
+  const auto bw = args::get(param::bw);
+  const auto bh = args::get(param::bw);
+  const auto ut = args::get(param::utime);
+
+  Enforce(cf.w == pf.w && cf.h == pf.h, "variable frame size is not allowed");
+  Enforce(cf.w > bw && cf.h > bh, "block size must be less than frame size");
+
+  static size_t cnt = 0;
+  static std::vector<double> probs;
+  if (cnt%ut == 0) {
+    probs.clear();
+    probs.resize((cf.w/bw) * (cf.h/bh));
+  }
+
+  double* prob = probs.data();
+  for (int32_t by = 0; by+bh < cf.h; by+=bh) {
+    for (int32_t bx = 0; bx+bw < cf.w; bx+=bw) {
+      *(prob++) += EachBlock(cf, pf, bx, by);
+    }
+  }
+
+  switch (args::get(param::output)) {
+  case param::kLen:
+  case param::kVec:
+    std::cout << std::endl;
+    break;
+  case param::kProb:
+    if ((cnt+1)%ut == 0) {
+      for (const auto prob : probs) {
+        std::cout << prob/(ut-1)/std::sqrt(2) << ' ';
+      }
+      std::cout << std::endl;
+    }
+    break;
+  default:
+    break;
+  }
+  ++cnt;
+}
+
+static void Exec() {
+  const auto bw = args::get(param::bw);
+  const auto bh = args::get(param::bw);
+  const auto ut = args::get(param::utime);
+  Enforce(bw > 0 && bh > 0, "block size must be greater than 0");
+  Enforce(ut > 0, "utime must be greater than 0");
+
+  const auto bmw  = args::get(param::bmw);
+  const auto bmh  = args::get(param::bmh);
+  const auto bmsw = args::get(param::bmw);
+  const auto bmsh = args::get(param::bmh);
+  Enforce(bmw > 0 && bmh > 0, "block matching region size must be greater than 0");
+  Enforce(bmsw > 0 && bmsh > 0, "block matching search region size must be greater than 0");
+
+  // open video stream
+  const auto vpath = args::get(param::vpath);
+  std::ifstream vst {vpath.c_str(), std::ifstream::binary | std::ifstream::ate};
+  Enforce(!!vst, "video stream is invalid");
+  const auto vsz = vst.tellg();
+
+  // init decoder
+  ISVCDecoder* dec;
+  WelsCreateDecoder(&dec);
+
+  SDecodingParam decp = {};
+  decp.sVideoProperty.eVideoBsType = VIDEO_BITSTREAM_DEFAULT;
+  decp.eEcActiveIdc                = ERROR_CON_SLICE_COPY;
+  dec->Initialize(&decp);
+
+  int declv = WELS_LOG_INFO;
+  dec->SetOption(DECODER_OPTION_TRACE_LEVEL, &declv);
+
+  uint8_t*    yuv[3] = {0};
+  SBufferInfo frame  = {};
+
+  // demux
+  MP4D_demux_t dem = {};
+  MP4D_open(&dem, [](int64_t off, void* buf, size_t sz, void* ptr) {
+    auto& vst = *reinterpret_cast<std::ifstream*>(ptr);
+    vst.seekg(off);
+    Enforce(!!vst, "seek failure");
+    vst.read(reinterpret_cast<char*>(buf), sz);
+    Enforce(!!vst, "read failure");
+    return 0;
+  }, &vst, vsz);
+
+  // find video track
+  int ti;
+  for (ti = 0; ti < dem.track_count; ++ti) {
+    const auto& t = dem.track[ti];
+    if (t.handler_type == MP4D_HANDLER_TYPE_VIDE) {
+      break;
+    }
+  }
+  Enforce(ti < dem.track_count, "no video track");
+  const auto& t = dem.track[ti];
+
+  // consume SPS
+  std::vector<uint8_t> nal;
+  for (size_t si = 0;; ++si) {
+    int sz;
+    auto sps = reinterpret_cast<const uint8_t*>(MP4D_read_sps(&dem, ti, si, &sz));
+    if (!sps) break;
+    CopyNal(nal, sps, sz);
+
+    const auto ret = dec->DecodeFrameNoDelay(nal.data(), nal.size(), yuv, &frame);
+    Enforce(ret == 0, "SPS decode failure");
+  }
+
+  // consume PPS
+  for (size_t si = 0;; ++si) {
+    int sz;
+    auto pps = reinterpret_cast<const uint8_t*>(MP4D_read_pps(&dem, ti, si, &sz));
+    if (!pps) break;
+    CopyNal(nal, pps, sz);
+
+    const auto ret = dec->DecodeFrameNoDelay(nal.data(), nal.size(), yuv, &frame);
+    Enforce(ret == 0, "PPS decode failure");
+  }
+
+  // decode frame
+  Frame pf = {};
+  size_t fidx = 0;
+  for (size_t si = 0; si < t.sample_count; ++si) {
+    unsigned fsz, time, dur;
+    const auto off = MP4D_frame_offset(&dem, ti, si, &fsz, &time, &dur);
+
+    vst.seekg(off);
+    Enforce(!!vst, "NAL seek failure");
+
+    nal.resize(fsz);
+    vst.read(reinterpret_cast<char*>(nal.data()), fsz);
+    Enforce(!!vst, "NAL read failure");
+
+    for (size_t i = 0; i < nal.size();) {
+      uint32_t sz =
+          (nal[i] << 24) | (nal[i+1] << 16) | (nal[i+2] << 8) | nal[i+3];
+
+      nal[i+0] = 0;
+      nal[i+1] = 0;
+      nal[i+2] = 0;
+      nal[i+3] = 1;
+      sz += 4;
+
+      const auto ret = dec->DecodeFrameNoDelay(&nal[i], fsz, yuv, &frame);
+      Enforce(ret == 0, "frame decode failure");
+
+      Frame cf = {yuv, frame};
+      if (fidx%ut > 0) {
+        EachFrame(cf, pf);
+      }
+      pf = std::move(cf);
+
+      ++fidx;
+      i += sz;
+    }
+  }
+}
+
+int main(int argc, char** argv)
+try {
+  param::parser.ParseCLI(argc, argv);
+  Exec();
+  return EXIT_SUCCESS;
+} catch (const args::Help&) {
+  std::cout << param::parser << std::endl;
+  return EXIT_SUCCESS;
+} catch (const std::exception& e) {
+  std::cerr << e.what() << std::endl;
+  return EXIT_FAILURE;
+}
+
+
+Frame::Frame(uint8_t* yuv[3], const SBufferInfo& frame) {
+  w = static_cast<int32_t>(frame.UsrData.sSystemBuffer.iWidth);
+  h = static_cast<int32_t>(frame.UsrData.sSystemBuffer.iHeight);
+  hw = w/2;
+  hh = h/2;
+
+  const auto ystride  = static_cast<int32_t>(frame.UsrData.sSystemBuffer.iStride[0]);
+  const auto uvstride = static_cast<int32_t>(frame.UsrData.sSystemBuffer.iStride[1]);
+
+  Y.resize(w*h);
+  for (int32_t y = 0; y < h; ++y) {
+    const auto src = yuv[0]   + y*ystride;
+    const auto dst = Y.data() + y*w;
+    std::memcpy(dst, src, w);
+  }
+
+  U.resize(hw*hh);
+  V.resize(hw*hh);
+  for (int32_t y = 0; y < hh; ++y) {
+    const auto offset = y*uvstride;
+    const auto srcu = yuv[0]   + y*uvstride;
+    const auto srcv = yuv[1]   + y*uvstride;
+    const auto dstu = U.data() + y*hw;
+    const auto dstv = V.data() + y*hw;
+    std::memcpy(dstu, srcu, hw);
+    std::memcpy(dstv, srcv, hw);
+  }
+}
+
+static void CopyNal(std::vector<uint8_t>& v, const uint8_t* buf, size_t sz) noexcept {
+  v.resize(sz+4);
+  v[0] = 0;
+  v[1] = 0;
+  v[2] = 0;
+  v[3] = 1;
+  std::memcpy(&v[4], buf, sz);
+}
diff --git a/thirdparty/CMakeLists.txt b/thirdparty/CMakeLists.txt
new file mode 100644
index 0000000..259af91
--- /dev/null
+++ b/thirdparty/CMakeLists.txt
@@ -0,0 +1,36 @@
+set(CMAKE_POLICY_DEFAULT_CMP0077 NEW)
+include(FetchContent)
+
+
+# ---- args ----
+# repository: https://github.com/Taywee/args
+# license   : MIT
+
+FetchContent_Declare(
+  args
+  URL "https://github.com/Taywee/args/archive/refs/tags/6.3.0.zip"
+)
+
+set(ARGS_BUILD_EXAMPLE   OFF)
+set(ARGS_BUILD_UNITTESTS OFF)
+FetchContent_MakeAvailable(args)
+
+
+# ---- minimp4 ----
+# repository: https://github.com/lieff/minimp4
+# license   : CC0
+
+FetchContent_Declare(
+  minimp4
+  URL "https://github.com/lieff/minimp4/archive/4575afb4f69ace25a1a048e25cc86bf8c8d14f2b.zip"
+)
+FetchContent_Populate(minimp4)
+
+add_library(minimp4)
+target_include_directories(minimp4 PUBLIC SYSTEM ${minimp4_SOURCE_DIR})
+target_sources(minimp4
+  PUBLIC
+    "${minimp4_SOURCE_DIR}/minimp4.h"
+  PRIVATE
+    minimp4.c
+)
diff --git a/thirdparty/minimp4.c b/thirdparty/minimp4.c
new file mode 100644
index 0000000..909b403
--- /dev/null
+++ b/thirdparty/minimp4.c
@@ -0,0 +1,2 @@
+#define MINIMP4_IMPLEMENTATION
+#include <minimp4.h>