Cross compiling OpenCV with ffmpeg

Question

I am trying to cross compile OpenCV 3.2 with ffpmeg from sources for armhf architecture on Ubuntu amd64. I have installed libraries for ffmpeg using

    sudo apt-get install libavcodec-dev:armhf libavformat-dev:armhf libswscale-dev:armhf
    sudo apt-get install libjpeg-dev:armhf libpng-dev:armhf libtiff-dev:armhf libjasper-dev:armhf

After cloning OpenCV from github I ran cmake with following command

    cmake -DENABLE_NEON=ON -DENABLE_VFPV3=ON -DWITH_FFMPEG=ON  -DCMAKE_TOOLCHAIN_FILE=../opencv/platforms/linux/arm-gnueabi.toolchain.cmake ../opencv

The output shows that all of the installed libraries can not be found. I don't know how to resolve this. There are also two folders which store armhf libs /usr/arm-linux-gnueabihf/lib and /usr/lib/arm-linux-gnueabihf so I am not sure if cmake is looking in the right directory and how to change that. Toolchain files look like this

arm-gnueabi.toolchain.cmake

    set(GCC_COMPILER_VERSION "" CACHE STRING "GCC Compiler version")
    set(GNU_MACHINE "arm-linux-gnueabi" CACHE STRING "GNU compiler triple")
    include("${CMAKE_CURRENT_LIST_DIR}/arm.toolchain.cmake")

arm.toolchain.cmake

if(COMMAND toolchain_save_config)
  return() # prevent recursive call
endif()

set(CMAKE_SYSTEM_NAME Linux)
set(CMAKE_SYSTEM_VERSION 1)
if(NOT DEFINED CMAKE_SYSTEM_PROCESSOR)
  set(CMAKE_SYSTEM_PROCESSOR arm)
else()
  #message("CMAKE_SYSTEM_PROCESSOR=${CMAKE_SYSTEM_PROCESSOR}")
endif()

include("${CMAKE_CURRENT_LIST_DIR}/gnu.toolchain.cmake")

if(CMAKE_SYSTEM_PROCESSOR STREQUAL arm AND NOT ARM_IGNORE_FP)
  set(FLOAT_ABI_SUFFIX "")
  if(NOT SOFTFP)
    set(FLOAT_ABI_SUFFIX "hf")
  endif()
endif()

if(NOT "x${GCC_COMPILER_VERSION}" STREQUAL "x")
  set(__GCC_VER_SUFFIX "-${GCC_COMPILER_VERSION}")
endif()

if(NOT DEFINED CMAKE_C_COMPILER)
  find_program(CMAKE_C_COMPILER NAMES ${GNU_MACHINE}${FLOAT_ABI_SUFFIX}-gcc${__GCC_VER_SUFFIX})
else()
  #message(WARNING "CMAKE_C_COMPILER=${CMAKE_C_COMPILER} is defined")
endif()
if(NOT DEFINED CMAKE_CXX_COMPILER)
  find_program(CMAKE_CXX_COMPILER NAMES ${GNU_MACHINE}${FLOAT_ABI_SUFFIX}-g++${__GCC_VER_SUFFIX})
else()
  #message(WARNING "CMAKE_CXX_COMPILER=${CMAKE_CXX_COMPILER} is defined")
endif()
if(NOT DEFINED CMAKE_LINKER)
  find_program(CMAKE_LINKER NAMES ${GNU_MACHINE}${FLOAT_ABI_SUFFIX}-ld${__GCC_VER_SUFFIX} ${GNU_MACHINE}${FLOAT_ABI_SUFFIX}-ld)
else()
  #message(WARNING "CMAKE_LINKER=${CMAKE_LINKER} is defined")
endif()
if(NOT DEFINED CMAKE_AR)
  find_program(CMAKE_AR NAMES ${GNU_MACHINE}${FLOAT_ABI_SUFFIX}-ar${__GCC_VER_SUFFIX} ${GNU_MACHINE}${FLOAT_ABI_SUFFIX}-ar)
else()
  #message(WARNING "CMAKE_AR=${CMAKE_AR} is defined")
endif()

if(NOT DEFINED ARM_LINUX_SYSROOT AND DEFINED GNU_MACHINE)
  set(ARM_LINUX_SYSROOT /usr/lib/${GNU_MACHINE}${FLOAT_ABI_SUFFIX})
endif()

if(NOT DEFINED CMAKE_CXX_FLAGS)
  set(CMAKE_CXX_FLAGS           "" CACHE INTERAL "")
  set(CMAKE_C_FLAGS             "" CACHE INTERAL "")
  set(CMAKE_SHARED_LINKER_FLAGS "" CACHE INTERAL "")
  set(CMAKE_MODULE_LINKER_FLAGS "" CACHE INTERAL "")
  set(CMAKE_EXE_LINKER_FLAGS    "" CACHE INTERAL "")

  set(CMAKE_CXX_FLAGS           "${CMAKE_CXX_FLAGS} -fdata-sections -Wa,--noexecstack -fsigned-char -Wno-psabi")
  set(CMAKE_C_FLAGS             "${CMAKE_C_FLAGS} -fdata-sections -Wa,--noexecstack -fsigned-char -Wno-psabi")
  if(CMAKE_SYSTEM_PROCESSOR STREQUAL arm)
    set(CMAKE_CXX_FLAGS           "-mthumb ${CMAKE_CXX_FLAGS}")
    set(CMAKE_C_FLAGS             "-mthumb ${CMAKE_C_FLAGS}")
    set(CMAKE_EXE_LINKER_FLAGS    "${CMAKE_EXE_LINKER_FLAGS} -Wl,-z,nocopyreloc")
  endif()
  if(CMAKE_SYSTEM_PROCESSOR STREQUAL arm)
    set(ARM_LINKER_FLAGS "-Wl,--fix-cortex-a8 -Wl,--no-undefined -Wl,--gc-sections -Wl,-z,noexecstack -Wl,-z,relro -Wl,-z,now")
  elseif(CMAKE_SYSTEM_PROCESSOR STREQUAL aarch64)
    set(ARM_LINKER_FLAGS "-Wl,--no-undefined -Wl,--gc-sections -Wl,-z,noexecstack -Wl,-z,relro -Wl,-z,now")
  endif()
  set(CMAKE_SHARED_LINKER_FLAGS "${ARM_LINKER_FLAGS} ${CMAKE_SHARED_LINKER_FLAGS}")
  set(CMAKE_MODULE_LINKER_FLAGS "${ARM_LINKER_FLAGS} ${CMAKE_MODULE_LINKER_FLAGS}")
  set(CMAKE_EXE_LINKER_FLAGS    "${ARM_LINKER_FLAGS} ${CMAKE_EXE_LINKER_FLAGS}")
else()
  #message(WARNING "CMAKE_CXX_FLAGS='${CMAKE_CXX_FLAGS}' is defined")
endif()

if(USE_NEON)
  message(WARNING "You use obsolete variable USE_NEON to enable NEON instruction set. Use -DENABLE_NEON=ON instead." )
  set(ENABLE_NEON TRUE)
elseif(USE_VFPV3)
  message(WARNING "You use obsolete variable USE_VFPV3 to enable VFPV3 instruction set. Use -DENABLE_VFPV3=ON instead." )
  set(ENABLE_VFPV3 TRUE)
endif()

set(CMAKE_FIND_ROOT_PATH ${CMAKE_FIND_ROOT_PATH} ${ARM_LINUX_SYSROOT})

    if(EXISTS ${CUDA_TOOLKIT_ROOT_DIR})
      set(CMAKE_FIND_ROOT_PATH ${CMAKE_FIND_ROOT_PATH} ${CUDA_TOOLKIT_ROOT_DIR})
    endif()

    set(TOOLCHAIN_CONFIG_VARS ${TOOLCHAIN_CONFIG_VARS}
        ARM_LINUX_SYSROOT
        ENABLE_NEON
        ENABLE_VFPV3
        CUDA_TOOLKIT_ROOT_DIR
    )
    toolchain_save_config()

Dr Yuan Shenghai Dr Yuan Shenghai · Accepted Answer · 2019-05-23T23:29:03

CMake uses Pkgconfig tool to find FFMPEG libraries and headers. The best way in your case to create pc file for your cross compiled FFMPEG and place it in pkgconfig folder of your cross compile environment.

try this export PKG_CONFIG_PATH=/usr/local/lib/pkgconfig also remember to rm CMakeCache.txt.

If you use cross compile tool chain from Ubuntu repositories, then place everything in /usr/arm-linux-gnueabi(hf)/

Cross compiling OpenCV with ffmpeg

1 Answers