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• Use FFMPEG in OpenCV without internet connection

  17 novembre 2022, par Henalds

  I am creating a project in c++ with QtCreator (5.14.1, MingGW compiler) and trying to use OpenCv (3.4.16) to read video files. I have tried many files of standard formats and codecs (H.264, yuv420, .mov etc). However, no matter what I try, VideoCapture() always silently fails. It doesn’t crash or show any error code, instead isOpened() is just always false.

  


  I think the cause is that I am building opencv (via this tutorial https://wiki.qt.io/How_to_setup_Qt_and_openCV_on_Windows) without internet connection (I cannot have internet connection on this machine, so please do not ask me to) and therefore it can’t download the FFMPEG libraries during this process. I have been looking everywhere for information about how to download the FFMPEG libraries for opencv directly but I haven’t had any luck.

  


  Can someone please explain what libraries I need to download and how opencv goes about looking for them ? because at the moment I don’t know what I need, nor where to put them, and I cant find any information on the topic.

  


  Or, can someone explain why calling VideoCapture(“video.mov”, cv::CAP_ANY) doesn’t have any effect ? (despite being able to play the video easily in VLC, MediaPlayer etc).

  


  Code :
`

  


  int main()
{
    VideoCapture cap(“C://video.mov”);
    //VideoCapture cap(“C:/video.mov”);
    //VideoCapture cap(“C:\video.mov”);
    //VideoCapture cap(“C:\video.mov”);

    if (!cap.isOpened()){
        cout << "Error opening video stream or file"<< endl;
        return -1;
    }
}


  


  `

  


  I have tried downloading some ffmpeg DLLs and the EXEs and adding them to the PATH, no success. I have also tried downloading the shared GPL of ffmpeg (that comes with the libs and include) and added them my .pro file but no change in VideoCapture behavior.

  


  I have also tried moving the opencv_ffmpeg_64.dll (found in opencv/build/bin) to my executable directory but that didn't fix anything.

  


• Undefined Referernce Errors FFMPEG + QT + Ubuntu 12.04.2 LTS

  19 juillet 2013, par Cits

  i have 2 machines with Ubuntu 12.04.2 LTS (64 mb) and the other is a snow leopard OS.
  In my mac i work with ffmpeg without any trouble but then i try to use ffmpeg in ubuntu and 6700 (!) errors appear :

  error: undefined reference to `av_freep'
  
  error: undefined reference to `av_strstart'
  
  error: undefined reference to `av_freep'
  
  ...

  I use QT 4.8.5 and g++ x86 64b
  I installed ffmpeg following http://ffmpeg.org/trac/ffmpeg/wiki/UbuntuCompilationGuide without errors or warnings.

  My test code is :

  .h

  QT += core gui 
  
  
  
  INCLUDEPATH += \
  
      /usr/local/Include
  
  
  
  LIBS += /usr/local/lib/libavcodec.a
  
  LIBS += /usr/local/lib/libavutil.a
  
  LIBS += /usr/local/lib/libavformat.a
  
  LIBS += /usr/local/lib/libswscale.a
  
  
  
  
  
  SOURCES += main.cpp

  .cpp :

  extern "C"
  
  {
  
  #ifndef __STDC_CONSTANT_MACROS
  
  #  define __STDC_CONSTANT_MACROS
  
  #endif
  
  
  
  #include "libavcodec/avcodec.h"
  
  #include "libavformat/avformat.h"
  
  }
  
  
  
  #include 
  
  
  
  int main()
  
  {
  
      AVFormatContext *pFormatCtx;
  
      av_register_all();
  
  
  
      const char* fil = "/home/cits/Desktop/movFile.mov";
  
  
  
      if(avformat_open_input(&pFormatCtx, fil, NULL, NULL)!=0)
  
      {
  
          return -1; // Couldn't open file
  
      }
  
  
  
      if(avformat_find_stream_info(pFormatCtx, NULL)<0)
  
      {
  
          return -1; // Couldn't find stream information
  
      }
  
  
  
      return 0;
  
  }

  Any ideas ??

  Thanks in advance.

• MobileVLC for Iphonesimulator

  4 octobre 2012, par lvreiny

  I'm trying to build mobilevlc for iphonesimulator. I follow the steps from vlc's wiki :

  $ git clone git://git.videolan.org/MobileVLC.git 
  
  $ cd MobileVLC 
  
  $ ./buildMobileVLC.sh

  It stucked at ffmpeg's configure, no response in terminal.
  Anyone has the same experience ? What could be the problem ?

  I'm using Mac OSX Lion 10.7.5, Xcode 4.5, and building MobileVLC for Iphonesimulator5.1