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Linker errors when building a simple c++ program with ffmpeg
15 février 2023, par Serban StoenescuI have this c++ program :


#include <iostream>

extern "C"
{
 #include <libavcodec></libavcodec>avcodec.h>
 #include <libavformat></libavformat>avformat.h>
 #include <libswscale></libswscale>swscale.h>

}

namespace hrean::ffmpeg
{
namespace detail
{
 
}//namespace detail

void testFFmpeg()
{
 AVFormatContext *avFormatContext = avformat_alloc_context();
 //I can comment out the rest of the function, the error is the same

} //testFFmpeg()

} //namespace hrean::ffmpeg


int main(int argc, char **argv)
{
 try
 {
 hrean::ffmpeg::testFFmpeg();
 }
 catch(const std::runtime_error& e)
 {
 std::cerr << "Error! " << e.what() << '\n';
 return -1;
 }
 catch(...)
 {
 std::cerr << "Unknown error\n";
 return -1;
 }
 
 return 0;
}
</iostream>

The CMakeLists.txt for this is :


cmake_minimum_required(VERSION 3.13)
project(hrean)

add_subdirectory(lib/ffmpeg-module)

message("[temp] FFMPEG_INCLUDE_DIRS = ${FFMPEG_INCLUDE_DIRS}")
message("[temp] FFMPEG_LIBRARIES = ${FFMPEG_LIBRARIES}")
add_executable(hrean-app src/main.cpp)
target_include_directories(hrean-app PUBLIC ${FFMPEG_INCLUDE_DIRS})
target_link_libraries(hrean-app PUBLIC ${FFMPEG_LIBRARIES})


The CMakeLists.txt for lib/ffmpeg-module contains only


find_package(FFmpeg REQUIRED MODULE)


The CMake output is :


-- The C compiler identification is GNU 11.3.0
-- The CXX compiler identification is GNU 11.3.0
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /usr/bin/cc - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Found PkgConfig: /usr/bin/pkg-config (found version "0.29.2") 
-- Checking for module 'libavcodec'
-- Found libavcodec, version 60.2.100
-- Checking for module 'libavformat'
-- Found libavformat, version 60.2.100
-- Checking for module 'libavdevice'
-- Found libavdevice, version 60.0.100
-- Checking for module 'libavutil'
-- Found libavutil, version 58.1.100
-- Checking for module 'libavfilter'
-- Found libavfilter, version 9.1.100
-- Checking for module 'libswscale'
-- Found libswscale, version 7.0.100
-- Checking for module 'libpostproc'
-- Found libpostproc, version 57.0.100
-- Checking for module 'libswresample'
-- Found libswresample, version 4.9.100
-- Found FFmpeg: /home/serban/ffmpeg_build/lib/libavcodec.a;/home/serban/ffmpeg_build/lib/libavformat.a;/home/serban/ffmpeg_build/lib/libavutil.a 
[temp] FFMPEG_INCLUDE_DIRS = /home/serban/ffmpeg_build/include
[temp] FFMPEG_LIBRARIES = /home/serban/ffmpeg_build/lib/libavcodec.a;/home/serban/ffmpeg_build/lib/libavformat.a;/home/serban/ffmpeg_build/lib/libavutil.a
-- Configuring done
-- Generating done
-- Build files have been written to: /home/serban/Work/hrean/build


When I run make, I get the following errors. The problem is, this worked perfectly yesterday and I changed nothing. I create a new Ubuntu virtual machine, everything fresh and I still get the same problem. The output is 1000+ lines long, here is some of it :


[ 50%] Building CXX object CMakeFiles/hrean-app.dir/src/main.cpp.o
[100%] Linking CXX executable hrean-app
/usr/bin/ld: /home/serban/ffmpeg_build/lib/libavformat.a(amvenc.o): in function `amv_write_packet':
/home/serban/ffmpeg/libavformat/amvenc.c:356: undefined reference to `av_packet_unref'
/usr/bin/ld: /home/serban/ffmpeg/libavformat/amvenc.c:357: undefined reference to `av_packet_ref'
/usr/bin/ld: /home/serban/ffmpeg_build/lib/libavformat.a(amvenc.o): in function `amv_deinit':
/home/serban/ffmpeg/libavformat/amvenc.c:209: undefined reference to `av_packet_free'
/usr/bin/ld: /home/serban/ffmpeg_build/lib/libavformat.a(amvenc.o): in function `amv_init':
/home/serban/ffmpeg/libavformat/amvenc.c:111: undefined reference to `avcodec_get_name'
/usr/bin/ld: /home/serban/ffmpeg/libavformat/amvenc.c:117: undefined reference to `avcodec_get_name'
/usr/bin/ld: /home/serban/ffmpeg/libavformat/amvenc.c:188: undefined reference to `av_new_packet'
/usr/bin/ld: /home/serban/ffmpeg/libavformat/amvenc.c:196: undefined reference to `av_packet_alloc'
/usr/bin/ld: /home/serban/ffmpeg_build/lib/libavformat.a(asfdec_o.o): in function `asf_read_close':
/home/serban/ffmpeg/libavformat/asfdec_o.c:1413: undefined reference to `av_packet_free'
/usr/bin/ld: /home/serban/ffmpeg_build/lib/libavformat.a(asfdec_o.o): in function `asf_read_single_payload':
/home/serban/ffmpeg/libavformat/asfdec_o.c:1119: undefined reference to `av_new_packet'
/usr/bin/ld: /home/serban/ffmpeg_build/lib/libavformat.a(asfdec_o.o): in function `asf_read_packet':
/home/serban/ffmpeg/libavformat/asfdec_o.c:1388: undefined reference to `av_packet_move_ref'
/usr/bin/ld: /home/serban/ffmpeg_build/lib/libavformat.a(asfdec_o.o): in function `reset_packet':
/home/serban/ffmpeg/libavformat/asfdec_o.c:1030: undefined reference to `av_packet_unref'
/usr/bin/ld: /home/serban/ffmpeg_build/lib/libavformat.a(asfdec_o.o): in function `asf_deinterleave':
/home/serban/ffmpeg/libavformat/asfdec_o.c:1313: undefined reference to `av_packet_unref'
/usr/bin/ld: /home/serban/ffmpeg/libavformat/asfdec_o.c:1314: undefined reference to `av_packet_from_data'
/usr/bin/ld: /home/serban/ffmpeg_build/lib/libavformat.a(asfdec_o.o): in function `asf_read_replicated_data':
/home/serban/ffmpeg/libavformat/asfdec_o.c:1043: undefined reference to `av_new_packet'
/usr/bin/ld: /home/serban/ffmpeg_build/lib/libavformat.a(asfdec_o.o): in function `asf_read_timestamp':
/home/serban/ffmpeg/libavformat/asfdec_o.c:1463: undefined reference to `av_packet_alloc'
/usr/bin/ld: /home/serban/ffmpeg_build/lib/libavformat.a(asfdec_o.o): in function `reset_packet':
/home/serban/ffmpeg/libavformat/asfdec_o.c:1030: undefined reference to `av_packet_unref'
/usr/bin/ld: /home/serban/ffmpeg_build/lib/libavformat.a(asfdec_o.o): in function `asf_read_timestamp':
/home/serban/ffmpeg/libavformat/asfdec_o.c:1512: undefined reference to `av_packet_unref'


Any idea how to debug this ?


Later edit :
This is the find script I am using : FindFFmpeg.cmake
I changed the way I link to the libraries, this way causes the least amount of errors :


set(ORDERED_FFMPEG_LIBRARIES ${AVFORMAT_LIBRARIES} ${AVCODEC_LIBRARIES} ${AVUTIL_LIBRARIES})
message("[temp] ORDERED_FFMPEG_LIBRARIES=${ORDERED_FFMPEG_LIBRARIES}")
add_executable(hrean-app src/main.cpp)

target_include_directories(hrean-app PUBLIC ${FFMPEG_INCLUDE_DIRS})
target_link_libraries(hrean-app PUBLIC ${ORDERED_FFMPEG_LIBRARIES})


The errors are similar, but they seem to point to other locations :


[100%] Linking CXX executable hrean-app
/usr/bin/ld: /home/serban/ffmpeg_build/lib/libavformat.a(mov.o): in function `mov_read_cmov':
/home/serban/ffmpeg/libavformat/mov.c:5578: undefined reference to `uncompress'
/usr/bin/ld: /home/serban/ffmpeg_build/lib/libavformat.a(swfdec.o): in function `swf_read_packet':
/home/serban/ffmpeg/libavformat/swfdec.c:393: undefined reference to `uncompress'
/usr/bin/ld: /home/serban/ffmpeg_build/lib/libavformat.a(swfdec.o): in function `swf_read_header':
/home/serban/ffmpeg/libavformat/swfdec.c:161: undefined reference to `inflateInit_'
/usr/bin/ld: /home/serban/ffmpeg_build/lib/libavformat.a(swfdec.o): in function `zlib_refill':
/home/serban/ffmpeg/libavformat/swfdec.c:134: undefined reference to `inflate'
/usr/bin/ld: /home/serban/ffmpeg_build/lib/libavformat.a(swfdec.o): in function `swf_read_close':
/home/serban/ffmpeg/libavformat/swfdec.c:557: undefined reference to `inflateEnd'


Do I have to link to anything else ?


Regards,
Serban


-
I'm trying to use FFmpeg with command prompt in my python program, but it doesnt execute [on hold]
26 mai 2018, par MilkToastI’ve tried to do it a bunch of different ways but each time it execute. The line works fine in the command prompt, but I cant get it to work from python.
check_output(r"ffmpeg -i C:\Users\jared\Desktop\Rev\videosnshit\howto.mp4 -vn -ar 44100 -ac 1 -b:a 32k -f wav audio.wav", shell=True)// This is the bit that works fine in command prompt :
ffmpeg -i C:\Users\jared\Desktop\Rev\videosnshit\howto.mp4 -vn -ar 44100 -ac 1 -b:a 32k -f wav audio.wavI’m probably being dumb, so any help would be great ! thanks !
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