ffmpeg多個函數上的未定義引用

Question

我正在嘗試在Ubuntu上編譯使用ffmpeg的應用程序，並且遇到以下錯誤。

undefined reference to `av_write_image_line2'
undefined reference to `av_hwframe_transfer_data'
undefined reference to `av_hwdevice_get_hwframe_constraints'
undefined reference to `av_hwframe_get_buffer'
undefined reference to `av_hwdevice_ctx_create_derived'
undefined reference to `xcb_xfixes_get_cursor_image_cursor_image'
undefined reference to `xcb_xfixes_query_version'
undefined reference to `avpriv_slicethread_execute'
undefined reference to `avcodec_parameters_to_context'
undefined reference to `xcb_xfixes_get_cursor_image_reply'
undefined reference to `av_hwdevice_find_type_by_name'
undefined reference to `av_hwframe_map'
undefined reference to `av_spherical_tile_bounds'
undefined reference to `av_malloc_array'
undefined reference to `av_hwframe_transfer_get_formats'
undefined reference to `av_hwframe_ctx_alloc'
undefined reference to `xcb_shape_rectangles'
undefined reference to `av_stereo3d_type_name'
undefined reference to `avpriv_slicethread_free'
undefined reference to `avpriv_slicethread_create'
undefined reference to `xcb_xfixes_get_cursor_image'
undefined reference to `av_hwframe_ctx_init'
undefined reference to `avpriv_register_devices'
undefined reference to `av_hwframe_constraints_free'
undefined reference to `av_audio_fifo_peek_at'
undefined reference to `av_get_extended_channel_layout'
undefined reference to `av_hwframe_ctx_create_derived'
undefined reference to `xcb_xfixes_query_version_reply'
undefined reference to `av_mallocz_array'
undefined reference to `av_read_image_line2'

我有ffmpeg的版本：

ffmpeg version 4.1.3 Copyright (c) 2000-2019 the FFmpeg developers
built with gcc 5.4.0 (Ubuntu 5.4.0-6ubuntu1~16.04.11) 20160609
configuration: --enable-pic --pkg-config-flags=--static --extra-libs='-lpthread -lm'
libavutil      56. 22.100 / 56. 22.100
libavcodec     58. 35.100 / 58. 35.100
libavformat    58. 20.100 / 58. 20.100
libavdevice    58.  5.100 / 58.  5.100
libavfilter     7. 40.101 /  7. 40.101
libswscale      5.  3.100 /  5.  3.100
libswresample   3.  3.100 /  3.  3.100

在我的makefile文件中，我已將-lavutil -lavcodec -lavdevice -lavfilter -lavformat -lswresample -lswscale添加到鏈接步驟。

我究竟做錯了什么？ 這些在我擁有的ffmpeg版本中已棄用嗎？

Answer 1

ffmpeg標頭是純C標頭。 因此，如果要在C ++應用程序中使用它們，則需要在include語句前加上extern "C"聲明。 例如：

extern "C"
{
    #include <libavcodec/avcodec.h>
}

如果不清楚該聲明在做什么， 這里和這里都有很好的解釋。

Answer 2

這可能是由於您的編譯器無法找到所需組件的正確位置。 如果知道他們的下落，則可以嘗試使用“符號鏈接”將其鏈接到編譯器正在查看的目錄/位置。

例如：

在-s / path / of / the / library / path / you / want / it / to / be / found