Question

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.

Answer 1

Finally, fixed it. I did two steps and I’m not sure which one worked (heh):

1. Added the ‘.lib’ files as linker input dependencies
2. I picked up the Sept 7 build and made sure I have all the same build-date for the dll’s, libraries, and include files.

Everything appears to work fine now.