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• Including objects to a shared library from a C++ archive (.a)

  1er septembre 2021, par El Sampsa

  I am trying to include some object files into a shared library I am building. Take the following command (things in [ETC] have been omitted for brevity) :

  



  


  /usr/bin/c++ -fPIC -std=c++14 -pthread -Iinclude/ext/liveMedia -Iinclude/ext/groupsock [ETC] -g -shared -Wl,-soname,libValkka.so -o lib/libValkka.so CMakeFiles/Valkka.dir/src/avthread.cpp.o CMakeFiles/Valkka.dir/src/opengl.cpp.o [ETC] CMakeFiles/Valkka.dir/src/decoders.cpp.o -lX11 -lGLEW -lGLU -lGL -Wl,—whole-archive lib/libavcodec.a -Wl,—no-whole-archive

  


  



  So basically I am just creating a shared library where most of the objects come from my own source code (i.e. CMakeFiles/Valkka.dir/src/*.o), but some of them come from an external static library, located at "lib/libavcodec.a". I get the following error :

  



  


  /usr/bin/ld : lib/libavcodec.a(h264_cabac.o) : relocation R_X86_64_PC32 against symbol 'ff_h264_cabac_tables' can not be used when making a shared object ; recompile with -fPIC
 /usr/bin/ld : final link failed : Bad value
 collect2 : error : ld returned 1 exit status

  


  



  But that is so untrue ! I can extract "libavcodec.a" with

  



  ar x libavcodec.a


  



  And after that check that

  



  readelf --relocs h264_cabac.o | egrep '(GOT|PLT|JU?MP_SLOT)' 


  



  does give some **it :

  



  


  00000000175d 003100000004 R_X86_64_PLT32 0000000000000000 __stack_chk_fail - 4
 000000001926 003100000004 R_X86_64_PLT32 0000000000000000 __stack_chk_fail - 4

  
 


  ...

  


  



  As does

  



  objdump -r h264_cabac.o | grep -i "relocation"


  



  So, indeed, the object files in "libavcodec.a" have been compiled to get PIC (position independent code).

  



  Why does the linker believe otherwise !?

  



  Related links :

  



  How to include all objects of an archive in a shared object ?

  



  Linking archives (.a) into shared object (.so)

  



  Is there a way to determine that a .a or .so library has been compiled as position indepenent code ?

  



  How can I tell, with something like objdump, if an object file has been built with -fPIC ?

  


• Is it possible to change a google cloud function from Ubuntu 22 (default image) to Ubuntu 18 ?

  19 octobre 2023, par Asher A

  I created a google cloud function via the Firebase CLI. I wasn't initially aware of which runtime environment the function (2nd generation) I created would be running on, however, I noticed that it didn't have ffmpeg installed so I tried looking for the actual runtime env. I then encountered this : https://cloud.google.com/functions/docs/reference/system-packages#requesting_a_package and through additional searches understood that the default base image is now ubuntu 22 which doesn't have ffmpeg -> so I tried checking if I could switch back to Ubuntu 18 (I haven't figured out how, or if it's possible at all). Is it possible to switch images or at least installing ffmpeg in the runtime I'm using ?

  


• How can i forcing current frame to be encoded as intra frame using libavcodec

  14 avril 2021, par pensir

  I want to change gop dynamic to adapt to player. Smaller gop help for reduce first screen cost ; Big gop help to reduce bitrate to save bandwidth.

  


  I found nvenc has a function which can solve the problem above.
https://docs.nvidia.com/video-technologies/video-codec-sdk/nvenc-video-encoder-api-prog-guide/#forcing-current-frame-to-be-encoded-as-intra-frame

  


  But I'm using ffmpeg. Is there any similar function in ffmpeg ?