OpenCV/opencv/modules/videoio/cmake/detect_ffmpeg.cmake

# --- FFMPEG ---
if(NOT HAVE_FFMPEG AND OPENCV_FFMPEG_USE_FIND_PACKAGE)
  if(OPENCV_FFMPEG_USE_FIND_PACKAGE STREQUAL "1" OR OPENCV_FFMPEG_USE_FIND_PACKAGE STREQUAL "ON")
    set(OPENCV_FFMPEG_USE_FIND_PACKAGE "FFMPEG")
  endif()
  find_package(${OPENCV_FFMPEG_USE_FIND_PACKAGE}) # Required components: AVCODEC AVFORMAT AVUTIL SWSCALE
  if(FFMPEG_FOUND OR FFmpeg_FOUND)
    set(HAVE_FFMPEG TRUE)
  endif()
endif()

if(NOT HAVE_FFMPEG AND WIN32 AND NOT ARM AND NOT OPENCV_FFMPEG_SKIP_DOWNLOAD)
  include("${OpenCV_SOURCE_DIR}/3rdparty/ffmpeg/ffmpeg.cmake")
  download_win_ffmpeg(FFMPEG_CMAKE_SCRIPT)
  if(FFMPEG_CMAKE_SCRIPT)
    include("${FFMPEG_CMAKE_SCRIPT}")
    set(HAVE_FFMPEG TRUE)
    set(HAVE_FFMPEG_WRAPPER TRUE)
  endif()
endif()

set(_required_ffmpeg_libraries libavcodec libavformat libavutil libswscale)
set(_used_ffmpeg_libraries ${_required_ffmpeg_libraries})
if(NOT HAVE_FFMPEG AND PKG_CONFIG_FOUND)
  ocv_check_modules(FFMPEG libavcodec libavformat libavutil libswscale)
  if(FFMPEG_FOUND)
    ocv_check_modules(FFMPEG_libavresample libavresample) # optional
    if(FFMPEG_libavresample_FOUND)
      list(APPEND FFMPEG_LIBRARIES ${FFMPEG_libavresample_LIBRARIES})
      list(APPEND _used_ffmpeg_libraries libavresample)
    endif()
    set(HAVE_FFMPEG TRUE)
  else()
    set(_missing_ffmpeg_libraries "")
    foreach (ffmpeg_lib ${_required_ffmpeg_libraries})
      if (NOT FFMPEG_${ffmpeg_lib}_FOUND)
        list(APPEND _missing_ffmpeg_libraries ${ffmpeg_lib})
      endif()
    endforeach ()
    message(STATUS "FFMPEG is disabled. Required libraries: ${_required_ffmpeg_libraries}."
            " Missing libraries: ${_missing_ffmpeg_libraries}")
    unset(_missing_ffmpeg_libraries)
  endif()
endif()

#=================================
# Versions check.
if(HAVE_FFMPEG AND NOT HAVE_FFMPEG_WRAPPER)
  set(_min_libavcodec_version 54.35.0)
  set(_min_libavformat_version 54.20.4)
  set(_min_libavutil_version 52.3.0)
  set(_min_libswscale_version 2.1.1)
  set(_min_libavresample_version 1.0.1)
  foreach(ffmpeg_lib ${_used_ffmpeg_libraries})
    if(FFMPEG_${ffmpeg_lib}_VERSION VERSION_LESS _min_${ffmpeg_lib}_version)
      message(STATUS "FFMPEG is disabled. Can't find suitable ${ffmpeg_lib} library"
              " (minimal ${_min_${ffmpeg_lib}_version}, found ${FFMPEG_${ffmpeg_lib}_VERSION}).")
      set(HAVE_FFMPEG FALSE)
    endif()
  endforeach()
  if(NOT HAVE_FFMPEG)
    message(STATUS "FFMPEG libraries version check failed "
            "(minimal libav release 9.20, minimal FFMPEG release 1.1.16).")
  endif()
  unset(_min_libavcodec_version)
  unset(_min_libavformat_version)
  unset(_min_libavutil_version)
  unset(_min_libswscale_version)
  unset(_min_libavresample_version)
endif()

#==================================

if(HAVE_FFMPEG AND NOT HAVE_FFMPEG_WRAPPER AND NOT OPENCV_FFMPEG_SKIP_BUILD_CHECK)
  try_compile(__VALID_FFMPEG
      "${OpenCV_BINARY_DIR}"
      "${OpenCV_SOURCE_DIR}/cmake/checks/ffmpeg_test.cpp"
      CMAKE_FLAGS "-DINCLUDE_DIRECTORIES:STRING=${FFMPEG_INCLUDE_DIRS}"
                  "-DLINK_LIBRARIES:STRING=${FFMPEG_LIBRARIES}"
      OUTPUT_VARIABLE TRY_OUT
  )
  if(NOT __VALID_FFMPEG)
    # message(FATAL_ERROR "FFMPEG: test check build log:\n${TRY_OUT}")
    message(STATUS "WARNING: Can't build ffmpeg test code")
    set(HAVE_FFMPEG FALSE)
  endif()
endif()

#==================================
unset(_required_ffmpeg_libraries)
unset(_used_ffmpeg_libraries)

if(HAVE_FFMPEG_WRAPPER)
  ocv_add_external_target(ffmpeg "" "" "HAVE_FFMPEG_WRAPPER")
elseif(HAVE_FFMPEG)
  ocv_add_external_target(ffmpeg "${FFMPEG_INCLUDE_DIRS}" "${FFMPEG_LIBRARIES}" "HAVE_FFMPEG")
  set(__builtin_defines "")
  set(__builtin_include_dirs "")
  set(__builtin_libs "")
  set(__plugin_defines "")
  set(__plugin_include_dirs "")
  set(__plugin_libs "")
  if(HAVE_OPENCL)
    set(__opencl_dirs "")
    if(OPENCL_INCLUDE_DIRS)
      set(__opencl_dirs "${OPENCL_INCLUDE_DIRS}")
    elseif(OPENCL_INCLUDE_DIR)
      set(__opencl_dirs "${OPENCL_INCLUDE_DIR}")
    else()
      set(__opencl_dirs "${OpenCV_SOURCE_DIR}/3rdparty/include/opencl/1.2")
    endif()
    # extra dependencies for buildin code (OpenCL dir is required for extensions like cl_d3d11.h)
    # buildin HAVE_OPENCL is already defined through cvconfig.h
    list(APPEND __builtin_include_dirs "${__opencl_dirs}")

    # extra dependencies for
    list(APPEND __plugin_defines "HAVE_OPENCL")
    list(APPEND __plugin_include_dirs "${__opencl_dirs}")
  endif()

  # TODO: libva, d3d11

  if(__builtin_include_dirs OR __builtin_include_defines OR __builtin_include_libs)
    ocv_add_external_target(ffmpeg.builtin_deps "${__builtin_include_dirs}" "${__builtin_include_libs}" "${__builtin_defines}")
  endif()
  if(VIDEOIO_ENABLE_PLUGINS AND __plugin_include_dirs OR __plugin_include_defines OR __plugin_include_libs)
    ocv_add_external_target(ffmpeg.plugin_deps "${__plugin_include_dirs}" "${__plugin_include_libs}" "${__plugin_defines}")
  endif()
endif()