[FFmpeg-trac] #7059(undetermined:new): Compile error in ffmpeg git master with opencv 3.4.1

[FFmpeg]

#7059: Compile error in ffmpeg git master with opencv 3.4.1
-------------------------------------+-------------------------------------
             Reporter:  bermond      |                     Type:  defect
               Status:  new          |                 Priority:  normal
            Component:               |                  Version:
  undetermined                       |  unspecified
             Keywords:               |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------
 I'm getting the following error at configure time when trying to compile
 ffmpeg git-master with the newly released opencv 3.4.1:
 {{{
 ERROR: libopencv not found
 }}}

 Relevant `ffbuild/config.log` section:
 {{{
 In file included from /usr/include/opencv2/core/types_c.h:59:0,
                  from /usr/include/opencv2/core/core_c.h:48,
                  from /tmp/ffconf.Rgo00uNd/test.c:1:
 /usr/include/opencv2/core/cvdef.h:485:1: error: unknown type name
 'namespace'
  namespace cv {
  ^~~~~~~~~
 /usr/include/opencv2/core/cvdef.h:485:14: error: expected '=', ',', ';',
 'asm' or '__attribute__' before '{' token
  namespace cv {
               ^
 ERROR: libopencv not found
 }}}

 It compiles fine when using opencv 3.4.0.

 How to reproduce:
 {{{
 $ git clone https://git.ffmpeg.org/ffmpeg.git
 $ cd ffmpeg
 $ ./configure --enable-libopencv
 }}}

 A relevant [https://github.com/opencv/opencv/issues/10963 issue (#10963)]
 is opened at the official opencv github repository regarding the same
 error when compiling vlc. Here is a quote of opencv developer Alexander
 Alekhin when answering this issue: ''"OpenCV 3.x doesn't not support C
 compilation mode officially. There are still legacy C API calls (from
 OpenCV 1.x) but they should be compiled in C++ compilation mode".''

 '''System information:'''
 '''OS:''' Arch Linux x86_64
 '''Compiler:''' gcc 7.3.0
 '''FFmpeg:''' git master
 '''OpenCV:''' 3.4.1

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Ticket URL: <https://trac.ffmpeg.org/ticket/7059>
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