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• Need help correcting Access Violation with FFmpeg DLL

  26 septembre 2012, par James

  I'm trying to use the FFmpeg dll's using Visual Studio 2012 and I'm getting a run time access violation when I call avcodec_find_encoder. Here is the code :

  // TestFFmpeg.cpp : Defines the entry point for the console application.
  
  //
  
  
  
  #include "stdafx.h"
  
  
  
  extern "C" {
  
  #include "libavcodec\avcodec.h"
  
  #include "libavformat\avformat.h"
  
  }
  
  
  
  #define INBUF_SIZE 4096
  
  
  
  int _tmain(int argc, _TCHAR* argv[])
  
  {
  
      AVCodec *codec;
  
  
  
      const char *videoFilename = "C:\\Users\\Public\\Videos\\Sample Videos\\Wildlife.wmv";
  
  
  
      av_register_all(); // This works; however, no parameters or return values.
  
  
  
      codec = avcodec_find_encoder(CODEC_ID_WMV3);  // Run time Access Violation HERE
  
      if (!codec) {
  
      fprintf(stderr, "Codec not found\n");
  
          exit(1);
  
      }
  
  
  
      return 0;
  
  }

  Here is the error message :

  Unhandled exception at 0x75C18B60 (msvcrt.dll) in TestFFmpeg.exe : 0xC0000005 : Access violation reading location 0x00000049.

  The stack trace is :

      msvcrt.dll!_strcmp()    Unknown
  
      avcodec-54.dll!6a56caac()   Unknown
  
      [Frames below may be incorrect and/or missing, no symbols loaded for avcodec-54.dll]    
  
  >   TestFFmpeg.exe!wmain(int argc, wchar_t * * argv) Line 23    C++
  
      TestFFmpeg.exe!__tmainCRTStartup() Line 533 C
  
      TestFFmpeg.exe!wmainCRTStartup() Line 377   C
  
      kernel32.dll!@BaseThreadInitThunk@12()  Unknown
  
      ntdll.dll!___RtlUserThreadStart@8() Unknown
  
      ntdll.dll!__RtlUserThreadStart@8()  Unknown

  I'm guessing there's a problem with returning the codec pointer, but I'm new to C++ and have no idea how to correct it. I tried the cdecl, stdcall, and fastcall calling conventions — none corrected the issue. I'm using the latest 32-bit DLL from Zeranoe. Any suggestions ?

  EDIT :
  I've called other functions in the DLL and they work. For example, avformat_open_input works properly. I can pass parameters and the function returns a successful return value (0) and populates the format context structure. av_find_stream_info works as well. I still can't figure out why avcodec_find_decoder creates an access violation.

• avcodec/svq1enc : Workaround GCC bug 102513

  25 octobre 2022, par Andreas Rheinhardt

  avcodec/svq1enc : Workaround GCC bug 102513
  GCC 11 has a bug : When it creates clones of recursive functions
  
  (to inline some parameters), it clones a recursive function
  
  eight times by default, even when this exceeds the recursion
  
  depth. This happens with encode_block() in libavcodec/svq1enc.c
  
  where a parameter level is always in the range 0..5 ;
  
  but GCC 11 also creates functions corresponding to level UINT_MAX
  
  and UINT_MAX - 1 (on -O3 ; -O2 is fine).
  Using such levels would produce undefined behaviour and because
  
  of this GCC emits bogus -Warray-bounds warnings for these clones.
  Since commit d08b2900a9f0935959303da668cb00a8a7245228, certain
  
  symbols that are accessed like ff_svq1_inter_multistage_vlc[level]
  
  are declared with hidden visibility, which allows compilers
  
  to bake the offset implied by level into the instructions
  
  if level is a compile-time constant as it is in the clones.
  
  Yet this leads to insane offsets for level == UINT_MAX which
  
  can be incompatible with the supported offset ranges of relocations.
  
  This happens in the small code model (the default code model for
  
  AArch64).
  This commit therefore works around this bug by disabling cloning
  
  recursive functions for GCC 10 and 11. GCC 10 is affected by the
  
  underlying bug (see
  
  https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102513), so the workaround
  
  also targets it, although it only produces three versions of
  
  encode_block(), so it does not seem to trigger the actual issue here.
  The issue has been mitigated in GCC 12.1 (it no longer creates clones
  
  for impossible values ; see also commit
  
  1cb7fd317c84117bbb13b14851d62f77f57bb9ce), so the workaround
  
  does not target it.
  Reported-by : J. Dekker <jdek@itanimul.li>
  
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
  
  Signed-off-by : J. Dekker <jdek@itanimul.li>
  

  • [DH] libavcodec/svq1enc.c

• Revision 36538 : On ajoute en base hasaudio et hasvideo ’oui’ ou ’’ On détecte mieux les ...

  22 mars 2010, par kent1@… — Log

  On ajoute en base hasaudio et hasvideo ’oui’ ou
  On détecte mieux les codes audio et videos sur les flv