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• How do I properly link ffmpeg using CMake in my Flutter plugin on Linux ?

  7 avril 2022, par GroovinChip

  I've written a Flutter plugin for Linux that uses ffmpeg and I'm having trouble building my example app that uses the plugin. I keep getting errors that there are no matching calls to several ffmpeg functions, which I can actually click into and see. Why is this happening and what can I do to fix it ?

  


  Here is my plugin's CMakeLists.txt :

  


  cmake_minimum_required(VERSION 3.10)
set(PROJECT_NAME "thumblr_linux")
project(${PROJECT_NAME} LANGUAGES CXX)

# This value is used when generating builds using this plugin, so it must
# not be changed
set(PLUGIN_NAME "thumblr_linux_plugin")

add_subdirectory(FFmpeg)

add_library(${PLUGIN_NAME} SHARED
  "thumblr_linux_plugin.cc"
)
apply_standard_settings(${PLUGIN_NAME})
set_target_properties(${PLUGIN_NAME} PROPERTIES
  CXX_VISIBILITY_PRESET hidden)
target_compile_definitions(${PLUGIN_NAME} PRIVATE FLUTTER_PLUGIN_IMPL)
target_include_directories(${PLUGIN_NAME} INTERFACE
  "${CMAKE_CURRENT_SOURCE_DIR}/include")
target_link_libraries(${PLUGIN_NAME} PRIVATE flutter)
target_link_libraries(${PLUGIN_NAME} PRIVATE PkgConfig::GTK FFmpgeg)

# List of absolute paths to libraries that should be bundled with the plugin
set(thumblr_linux_bundled_libraries
  ""
  PARENT_SCOPE
)


  


  and here is my FFmpeg/CMakeLists.txt :

  


  cmake_minimum_required(VERSION 3.14)
project(FFmpeg)

find_package(PkgConfig REQUIRED)
pkg_check_modules(AVCODEC     REQUIRED IMPORTED_TARGET libavcodec)
pkg_check_modules(AVFORMAT    REQUIRED IMPORTED_TARGET libavformat)
pkg_check_modules(AVFILTER    REQUIRED IMPORTED_TARGET libavfilter)
pkg_check_modules(AVDEVICE    REQUIRED IMPORTED_TARGET libavdevice)
pkg_check_modules(AVUTIL      REQUIRED IMPORTED_TARGET libavutil)
pkg_check_modules(SWRESAMPLE  REQUIRED IMPORTED_TARGET libswresample)
pkg_check_modules(SWSCALE     REQUIRED IMPORTED_TARGET libswscale)

add_library(FFmpeg INTERFACE IMPORTED GLOBAL)

target_link_libraries(FFmpeg INTERFACE
    PkgConfig::AVCODEC
    PkgConfig::AVFORMAT
    PkgConfig::AVFILTER
    PkgConfig::AVDEVICE
    PkgConfig::AVUTIL
    PkgConfig::SWRESAMPLE
    PkgConfig::SWSCALE
)


  


  and here are the error messages I get when building :

  


  /home/parallels/flutter_projects/thumblr/thumblr_linux/example/linux/flutter/ephemeral/.plugin_symlinks/thumblr_linux/linux/thumblr_linux_plugin.cc:80:9: error: no matching function for call to 'avformat_open_input'
/home/parallels/flutter_projects/thumblr/thumblr_linux/example/linux/flutter/ephemeral/.plugin_symlinks/thumblr_linux/linux/thumblr_linux_plugin.cc:84:9: error: no matching function for call to 'avformat_find_stream_info'
/home/parallels/flutter_projects/thumblr/thumblr_linux/example/linux/flutter/ephemeral/.plugin_symlinks/thumblr_linux/linux/thumblr_linux_plugin.cc:88:5: error: no matching function for call to 'av_dump_format'
/home/parallels/flutter_projects/thumblr/thumblr_linux/example/linux/flutter/ephemeral/.plugin_symlinks/thumblr_linux/linux/thumblr_linux_plugin.cc:102:61: error: assigning to 'AVCodecContext *' from incompatible type 'AVCodecParameters *'
/home/parallels/flutter_projects/thumblr/thumblr_linux/example/linux/flutter/ephemeral/.plugin_symlinks/thumblr_linux/linux/thumblr_linux_plugin.cc:111:9: error: use of undeclared identifier 'avcodec_open'
/home/parallels/flutter_projects/thumblr/thumblr_linux/example/linux/flutter/ephemeral/.plugin_symlinks/thumblr_linux/linux/thumblr_linux_plugin.cc:119:14: error: use of undeclared identifier 'avcodec_alloc_frame'
/home/parallels/flutter_projects/thumblr/thumblr_linux/example/linux/flutter/ephemeral/.plugin_symlinks/thumblr_linux/linux/thumblr_linux_plugin.cc:122:17: error: use of undeclared identifier 'avcodec_alloc_frame'
/home/parallels/flutter_projects/thumblr/thumblr_linux/example/linux/flutter/ephemeral/.plugin_symlinks/thumblr_linux/linux/thumblr_linux_plugin.cc:127:16: error: no matching function for call to 'atk_image_get_image_size'
/home/parallels/flutter_projects/thumblr/thumblr_linux/example/linux/flutter/ephemeral/.plugin_symlinks/thumblr_linux/linux/thumblr_linux_plugin.cc:133:5: error: use of undeclared identifier 'av_image_fill_arrays'
/home/parallels/flutter_projects/thumblr/thumblr_linux/example/linux/flutter/ephemeral/.plugin_symlinks/thumblr_linux/linux/thumblr_linux_plugin.cc:144:9: error: use of undeclared identifier 'avcodec_decode_video'
/home/parallels/flutter_projects/thumblr/thumblr_linux/example/linux/flutter/ephemeral/.plugin_symlinks/thumblr_linux/linux/thumblr_linux_plugin.cc:179:15: error: unused variable 'ret' [-Werror,-Wunused-variable]
/home/parallels/flutter_projects/thumblr/thumblr_linux/example/linux/flutter/ephemeral/.plugin_symlinks/thumblr_linux/linux/thumblr_linux_plugin.cc:211:5: error: no matching function for call to 'avformat_close_input'


  


  the C++ code for the plugin itself can be found here : https://github.com/GroovinChip/thumblr/blob/main/thumblr_linux/linux/thumblr_linux_plugin.cc

  


• libavformat fails to link on Macos

  24 avril 2022, par Bilal Shafi

  I'm trying to go through an ffmpeg tutorial however when I try to build my project I get the following error. I initialy thought that cmake's find_path and find_library was linking the wrong files Mark Setchell showed that this was not the case. Now I'm not sure why the linker errors are occurring. Here is the minimum example that fails to compile and the aforementioned error.

  


  [build] [1/1 100% :: 0.076] Linking CXX executable example
[build] FAILED: example 
[build] : && /usr/bin/clang++ -g -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX12.1.sdk -Wl,-search_paths_first -Wl,-headerpad_max_install_names -L/usr/local/opt/llvm/lib CMakeFiles/example.dir/main.cpp.o -o example  /usr/local/lib/libavformat.dylib && :
[build] Undefined symbols for architecture x86_64:
[build]   "avformat_open_input(AVFormatContext**, char const*, AVInputFormat const*, AVDictionary**)", referenced from:
[build]       _main in main.cpp.o
[build]   "avformat_free_context(AVFormatContext*)", referenced from:
[build]       _main in main.cpp.o
[build]   "avformat_alloc_context()", referenced from:
[build]       _main in main.cpp.o
[build] ld: symbol(s) not found for architecture x86_64
[build] clang: error: linker command failed with exit code 1 (use -v to see invocation)
[build] ninja: build stopped: subcommand failed.


  


  CMakeLists.txt :

  


  cmake_minimum_required(VERSION 3.21)
set(CMAKE_CXX_STANDARD 17)


find_path(AVFORMAT_INCLUDE_DIRS libavformat/avformat.h REQUIRED)
find_library(AVFORMAT_LIBRARY avformat REQUIRED)

message(WARNING "AVFORMAT_LIBRARY=" ${AVFORMAT_LIBRARY})
message(WARNING "AVFORMAT_INCLUDE_DIRS=" ${AVFORMAT_INCLUDE_DIRS})

add_executable(example main.cpp)
target_link_libraries(example ${AVFORMAT_LIBRARY})
target_include_directories(example PRIVATE ${AVFORMAT_INCLUDE_DIRS})



  


  main.cpp :

  


  #include <libavformat></libavformat>avformat.h>&#xA;&#xA;#include &#xA;&#xA;&#xA;int main(int argc, char **argv) {&#xA;    if (argc &lt; 2) {&#xA;        printf("example ");&#xA;        exit(EXIT_FAILURE);&#xA;    }&#xA;&#xA;    AVFormatContext *pFormatContext = avformat_alloc_context();&#xA;&#xA;    avformat_open_input(&amp;pFormatContext, argv[1], nullptr, nullptr);&#xA;    printf("Format %s, duration %lld us", pFormatContext->iformat->long_name, pFormatContext->duration);&#xA;&#xA;&#xA;    avformat_free_context(pFormatContext);&#xA;}&#xA;

  


• yt-dlp get audio only link -> ffmpeg piped audio -> ffplay

  5 juin 2022, par james28909

  Ok, i have a perl script that i am trying to figure out why it is throwing an io error. First i use yt-dlg to get the link of only the audio - this works as expected and i can navigate to the link in a browser just fine. then i open a ffmpeg pipe in perl and then try to read the output from ffmpeg and eventually, if i can get this working, i will process the ffmpeg output then send to a named pipe.

  


  the problem comes from the ffmpeg when i am processing the data from the link obtained with yt-dlp, and i think it has to do with my while loop but i am not sure what. i have a named pipe called "input". i summon ffmpeg with the following :

  


  #/usr/bin/perl
use strict;
use warnings;

my $file = /path/to/named/pipe
my $read_len = 1024;

open (my $SOURCE_AUDIO, '-|', "ffmpeg -y -i \'$link\' -map 0 -c copy -ac 2 -f opus -ar 48000 pipe:1");
binmode($SOURCE_AUDIO);

# process the ffmpeg output.i have a function i want to implement here, 
# but i need to be able to parse ffmpeg output in set read lengths

while( read($SOURCE_AUDIO, my $buf, $read_len)){
print $file $buf;
};


  


  but before the end of the playback, somewhere around the end of the audio stream ffmpeg throws errors like this :

  


  [tls @ 0x5d0de00] Error in the pull function..2kbits/s speed=1.21x
[tls @ 0x5d0de00] IO error: Connection reset by peer
[tls @ 0x5d0de00] The specified session has been invalidated for some reason.
    Last message repeated 1 times
https://rr3---sn-(truncated): Input/output error
size=    1021kB time=00:01:18.36 bitrate= 106.7kbits/s speed=1.21x
video:0kB audio:1012kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.808163%


  


  i am not sure what is causing it to end early, or what is causing it to be terminated. i can download the file and re-encode it (if needed) and then play it flawlessly with ffplay, but i cannot, for the life of me, parse ffmpeg output and write it to a named pipe. any help sure would be appreciated. thanks

  


  P.S. i am using latest updated windows 11 and WSL's built in perl :

  


  This is perl 5, version 30, subversion 0 (v5.30.0) built for x86_64-linux-gnu-thread-multi
(with 50 registered patches, see perl -V for more detail)

Copyright 1987-2019, Larry Wall

Perl may be copied only under the terms of either the Artistic License or the
GNU General Public License, which may be found in the Perl 5 source kit.

Complete documentation for Perl, including FAQ lists, should be found on
this system using "man perl" or "perldoc perl".  If you have access to the
Internet, point your browser at http://www.perl.org/, the Perl Home Page.