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• 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.

• 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.

  


• ffmpeg playback problems when concatenating 2 gif of same type into 1 file without re-encoding [closed]

  15 juin 2022, par kite

  I see this information here, but it didn't help :
https://stackoverflow.com/a/11175851/11361179

  


  Given 2 gif files 1.gif 2.gif of same type, I want to merge them into a single .gif file and stream without re-encode. Following the instructions here https://trac.ffmpeg.org/wiki/Concatenate : I make a list in windows called mylist with the names, then I concatenate using the below. The file created only runs correctly in ffplay though, anywhere else it will simply repeat the first 1.gif over and over and not play the other.

  


  (for %i in (*.gif) do @echo file '%i') > mylist.txt
ffmpeg -f concat -i mylist.txt -c copy output.gif


  


  I downloaded the newest version of ffmpeg and it didn't change anything. I also tried : ffmpeg -i "concat:input1|input2" -codec copy output.mkv. No change. I need the output to play properly in programs other than ffplay.

  


  The file generated is of the same length as 1.gif rather than the combined, and seeking has issues in ffplay, so there seems to be an issue with the output not having the right metadata for proper playback. All 3 files are the exact same in ffprobe except their bitrate value, as they should be since both gif were taken in same program with same settings of same length....with the exception that the third gif should be the combined length which it isn't. Removing -c copy and re-encoding works but generates a gif 50x the size of horrid quality.