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• ffmpeg code does not link (undefined reference to avcodec_register_all

  28 janvier 2013, par Sriram

  I am trying to compile a simple introductory program using ffmpeg that tries to check if the mp3 codec is available. While the code compiles OK, I am facing difficulty in solving linker errors. Here is the code :

  #include 
  
  #include 
  
  #include <libavcodec></libavcodec>avcodec.h>
  
  
  
  float *generateSinusoid(unsigned int sampleRate, unsigned int nSecondsAudio) {
  
  
  
    unsigned int nsamples = (nSecondsAudio * sampleRate);
  
    float *arr;
  
    arr = (float*) malloc(sizeof(float) * nsamples);
  
    int i = 0;
  
  
  
    for(i = 0; i &lt; nsamples; i++) {
  
      arr[i] = 20 * sin(2.f * (M_PI) * (330/sampleRate) * i);  /*frequency of 330H
  
  z*/
  
    }
  
  
  
    return arr;
  
  
  
  }
  
  
  
  int main(int argc, char *argv[]) {
  
  
  
    avcodec_register_all();
  
  
  
    AVCodec *codec;
  
  
  
    unsigned int sampleRate = 22050;  /*assumed.*/
  
    unsigned int nSecondsAudio = 4;
  
    float *arr;
  
    arr = (float *) malloc(sizeof(float) * nSecondsAudio * sampleRate);
  
  
  
    /*Step 1. Generate sinusoid.*/
  
    arr = generateSinusoid(sampleRate, nSecondsAudio);
  
  
  
    /* Step 2. See if encoder exists.*/
  
    /*codec = avcodec_find_encoder(AV_CODEC_ID_MP3);*/
  
  
  
    if(!codec) {  /*codec = NULL.*/
  
      printf("MP3 codec not found!!!!");
  
    } else {
  
      printf("MP3 codec found!!!");
  
    }
  
  
  
     return 0;
  
  }  

  The code is compiled and linked like so :

  encoding_mp3: encoding_mp3.o
  
          gcc encoding_mp3.o -o encoding_mp3 -L/cygdrive/c/Users/Desktop/webserver/cygnus/lib/w32api -L/cygdrive/c/Users/Desktop/webserver/cygnus/ffmpeg/ffmpeg_dev/lib -lm -luser32 -lpthread -lavcodec
  
  
  
  encoding_mp3.o: encoding_mp3.c
  
          gcc -I/cygdrive/c/Users/Desktop/webserver/cygnus/ffmpeg/ffmpeg_dev/include -I/cygdrive/c/Users/Desktop/webserver/cygnus/usr/include -g -c encoding_mp3.c -o encoding_mp3.o
  
  
  
  clean:
  
          rm encoding_mp3.o encoding_mp3  

  Linking gives the following error :

  gcc -I/cygdrive/c/Users/Desktop/webserver/cygnus/ffmpeg/ffmpeg_dev/include -I/cygdrive/c/Users/Desktop/webserver/cygnus/usr/include -g -c encoding_mp3.c -o encoding_mp3.o
  
  gcc encoding_mp3.o -o encoding_mp3 -L/cygdrive/c/Users/Desktop/webserver/cygnus/lib/w32api -L/cygdrive/c/Users/Desktop/webserver/cygnus/ffmpeg/ffmpeg_dev/lib -lm -luser32 -lpthread -lavcodec
  
  encoding_mp3.o: In function `main':
  
  /cygdrive/c/Users/Desktop/webserver/cygnus/ffmpeg/work/encoding_mp3.c:31: undefined reference to `_avcodec_register_all'
  
  collect2: ld returned 1 exit status
  
  make: *** [encoding_mp3] Error 1  

  I have gone through most of the threads on SO regarding this problem and here is what I have tried so far :
  
   Put libraries at the end of all non-option arguments
  
   Commented out code that references functions. This seems to work. The undefined reference errors go away after all function calls are removed, though the presence of a struct AVCodec does not cause any problems.

  Any help on this is most welcome.

• CMake specifies link libraries in wrong order [duplicate]

  18 janvier 2021, par Jamie Royer

  I'm following a youtube video on building a project with CMake and FFmpeg. The author is using a Mac and I'm using Ubuntu 20.04. I've been following along successfully until hitting this problem. cmake —version returns 3.16.3

  


  For some reason it is specifying the libraries too early so nothing is imported :

  


  ~/video-app/build# cmake ..
~/video-app/build# make VERBOSE=1
...
/usr/bin/c++ \
   -lavcodec -lavformat \                            # << Too early
   CMakeFiles/video-app.dir/src/main.cpp.o \
   CMakeFiles/video-app.dir/src/load_frame.cpp.o \
   -o video-app \                                    # << Should be here
   lib/glfw/src/libglfw3.a \
   -lGL -lGLU -lpthread /usr/lib/x86_64-linux-gnu/librt.so -lm -ldl


  


  If I manually run the command with the -l (dash ell) reordered, it compiles successfully.

  


  Here is the contents of the two CMakeLists.txt files.

  


  # video-app/CMakeLists.txt
cmake_minimum_required(VERSION 3.14)
project(video-app C CXX)
set(CMAKE_CXX_STANDARD 14)
add_subdirectory(lib/glfw)
add_subdirectory(lib/FFmpeg)
list(APPEND EXTRA_LIBS "-lGL -lGLU")
list(APPEND SOURCES src/main.cpp src/load_frame.cpp)
add_executable(video-app ${SOURCES})
target_link_libraries(video-app FFmpeg glfw ${EXTRA_LIBS})


  


  # video-app/lib/CMakeLists.txt
cmake_minimum_required(VERSION 3.14)
project(FFmpeg)
find_package(PkgConfig REQUIRED)
# There are seven libraries in original - only two shown here for brevity.
pkg_check_modules(AVCODEC   REQUIRED IMPORTED_TARGET libavcodec)
pkg_check_modules(AVFORMAT  REQUIRED IMPORTED_TARGET libavformat)
add_library(FFmpeg INTERFACE IMPORTED GLOBAL)
target_include_directories(FFmpeg INTERFACE
    ${AVCODEC_INCLUDE_DIRS}
    ${AVFORMAT_INCLUDE_DIRS})
target_link_options(FFmpeg INTERFACE
    ${AVCODEC_LDFLAGS}
    ${AVFORMAT_LDFLAGS})


  


  I tried :

  


  

  • Changing the order of target_link_libraries in top CMake file. Funny thing is, it worked once.

  


  • I tried adding target_link_libraries to FFmpeg CMake file.

  


  • Searching for stackover.com for answers and reading CMake documentation.

  


  


• Cannot link with libswscale properly using cmake. Undefined symbols for architecture x86_64 : sws_getContext()

  8 novembre 2022, par J. Johnson

  I'm building a small project that will output video. I'm trying to link to libswscale to convert RGBA to YUV420, however, the linker ld cannot successfully find libswscale symbols.

  


  Undefined symbols for architecture x86_64:
  "sws_getContext(int, int, AVPixelFormat, int, int, AVPixelFormat, int, SwsFilter*, SwsFilter*, double const*)", referenced from:
      VideoWriter::writeFrame(std::__1::vector >) in video_writer.cpp.o


  


  The offending line of code is this.

  


  struct SwsContext *sws_ctx = sws_getContext(
    avCodecContext->width, avCodecContext->height, AV_PIX_FMT_RGBA,
    avCodecContext->width, avCodecContext->height, AV_PIX_FMT_YUV420P,
    SWS_BILINEAR, NULL, NULL, NULL);


  


  When I use -v on clang I see that the libswscale.dylib is being passed to ld. The dylib exists on the file system and is the same version as the library's header, as verified by otool.

  


   "/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ld" -demangle -lto_library /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/libLTO.dylib -no_deduplicate -dynamic -arch x86_64 -platform_version macos 10.15.0 11.1 -syslibroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX11.1.sdk -o bin/main -search_paths_first -headerpad_max_install_names CMakeFiles/main.dir/src/main.cpp.o CMakeFiles/main.dir/src/window.cpp.o CMakeFiles/main.dir/src/video_writer.cpp.o -rpath /usr/local/lib /usr/local/lib/libGLEW.2.2.0.dylib /usr/local/lib/libboost_program_options-mt.dylib -framework OpenGL /usr/local/Cellar/sdl2_image/2.6.2/lib/libSDL2_image.dylib /usr/local/lib/libSDL2.dylib /usr/local/Cellar/ffmpeg/5.1.2/lib/libavcodec.dylib /usr/local/Cellar/ffmpeg/5.1.2/lib/libswscale.dylib /usr/local/Cellar/ffmpeg/5.1.2/lib/libavutil.dylib -lc++ -lSystem /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/12.0.0/lib/darwin/libclang_rt.osx.a -F/Library/Developer/CommandLineTools/SDKs/MacOSX10.15.sdk/System/Library/Frameworks


  


  This is my cmake file.

  


  cmake_minimum_required(VERSION 3.19.2)

project(FragTool VERSION 1.0)

set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} "${CMAKE_SOURCE_DIR}/cmake/")

# --- c++ build settings --- #
set(CMAKE_CXX_STANDARD 11)
set(CMAKE_CXX_STANDARD_REQUIRED True)
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Weffc++ -O0")
set(CMAKE_ARCHIVE_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/lib)
set(CMAKE_LIBRARY_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/lib)
set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/bin)

set(CMAKE_BUILD_TYPE Debug)

# --- dependencies --- #
find_package(GLEW REQUIRED)
find_package(Boost 1.79.0 COMPONENTS program_options REQUIRED)

find_package(PkgConfig REQUIRED)
pkg_check_modules(LIBAV REQUIRED IMPORTED_TARGET
    libavcodec
    libswscale
    libavutil
)

pkg_check_modules(LIBSDL2 REQUIRED IMPORTED_TARGET
    sdl2
    sdl2_image
)

set(EXECUTABLE main)
add_executable(${EXECUTABLE} src/main.cpp)
target_sources(${EXECUTABLE} PRIVATE
    ${CMAKE_SOURCE_DIR}/src/window.cpp
    ${CMAKE_SOURCE_DIR}/src/video_writer.cpp
)

target_include_directories(${EXECUTABLE} PRIVATE ${CMAKE_SOURCE_DIR}/src)
target_include_directories(${EXECUTABLE} PRIVATE ${GLEW_INCLUDE_DIRS})

target_link_libraries(${EXECUTABLE} PRIVATE GLEW::glew)
target_link_libraries(${EXECUTABLE} PRIVATE ${Boost_LIBRARIES})
target_link_libraries(${EXECUTABLE} PRIVATE PkgConfig::LIBSDL2)
target_link_libraries(${EXECUTABLE} PRIVATE PkgConfig::LIBAV)


  


  I'm stumped as to what could be causing the linker to fail, given that it is being passed the libswscale dylib correctly as far as I can tell. I checked for any other versions of the dylib on the system that maybe are shadowing it, but didn't see any.