[libav-api] Linking errors with mingw

Brian Mearns bmearns at ieee.org
Thu Oct 17 16:44:23 CEST 2013


I'm trying to build a very minimal program from the ffmpeg src
distributions examples, and it seems it can't find any of the libav*
functions.

I'm running windows 7 (64-bit) and mingw gcc version 4.7.1.

I've just downloaded version 9.7 of libav from
http://win32.libav.org/releases/libav-9.7-win64.7z, and unpacked it so that
bin/, include/, lib/, and share/ are all under C:\apps\pf\libav\.

>From the ffmpeg examples (external to libav), I can run pkg-config and get
the options for libav, and I use the following commands to compile and
link, respectively:

>gcc -o metadata.obj -c -IC:\apps\pf\libav\include metadata.c

>gcc -o metadata.exe metadata.obj -LC:\apps\pf\libav\lib -lavutil
-lavdevice -lavformat -lavfilter -lavcodec -lavresample -lswscale

The compile goes fine, but linking produces the following errors:

metadata.obj:metadata.c:(.text+0x44): undefined reference to
`av_register_all'
metadata.obj:metadata.c:(.text+0x6c): undefined reference to
`avformat_open_input'
metadata.obj:metadata.c:(.text+0xcb): undefined reference to `av_dict_get'
metadata.obj:metadata.c:(.text+0xe2): undefined reference to
`avformat_close_input'
collect2.exe: error: ld returned 1 exit status

All four libav functions that are called from the source cannot be found by
the linker, but notice it was able to find the specified libraries
themselves, otherwise it would complain about that.

I get the same behavior using libav and the libraries that come with
Zeranoe's ffmpeg dev build for windows (http://ffmpeg.zeranoe.com/builds/),
and it's driving me nuts! Can any one help me link against these libs using
mingw?

The complete contents of the metadata.c file are included at the end of the
message.

Thanks,
-Brian


//////////////////////////////// metadata.c
//////////////////////////////////

/*
 * Copyright (c) 2011 Reinhard Tartler
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
copy
 * of this software and associated documentation files (the "Software"), to
deal
 * in the Software without restriction, including without limitation the
rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included
in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR
OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

/**
 * @file
 * Shows how the metadata API can be used in application programs.
 * @example doc/examples/metadata.c
 */

#include <stdio.h>

#include <libavformat/avformat.h>
#include <libavutil/dict.h>

int main (int argc, char **argv)
{
    AVFormatContext *fmt_ctx = NULL;
    AVDictionaryEntry *tag = NULL;
    int ret;

    if (argc != 2) {
        printf("usage: %s <input_file>\n"
               "example program to demonstrate the use of the libavformat
metadata API.\n"
               "\n", argv[0]);
        return 1;
    }

    av_register_all();
    if ((ret = avformat_open_input(&fmt_ctx, argv[1], NULL, NULL)))
        return ret;

    while ((tag = av_dict_get(fmt_ctx->metadata, "", tag,
AV_DICT_IGNORE_SUFFIX)))
        printf("%s=%s\n", tag->key, tag->value);

    avformat_close_input(&fmt_ctx);
    return 0;
}

////////////////////////////// end metadata.c
/////////////////////////////////


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