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• OpenCV no longer working after Homebrew install

  28 mars 2014, par Tom smith

  I have have been running OpenCV from QT creator on Mac OSX.
  I was having trouble getting VideoWriter to work so it was suggested I try installing ffmpeg with opencv.
  Using brew I executed this command

  brew install homebrew/science/opencv --with-ffmpeg 

  However, during this process I received the following error

  Warning: Could not link opencv. Unlinking...
  
  Error: The `brew link` step did not complete successfully
  
  The formula built, but is not symlinked into /usr/local
  
  You can try again using `brew link opencv'

  The "possible conflicting files were mostly from "/usr/local/include/opencv2/"

  I tried the command brew suggested but this gave me a permission denied warning so I found a fix to execute before the command, both of which are below.

  sudo chown -R `whoami` /usr/local
  
  brew link --overwrite opencv

  This appeared to execute correctly giving me the following response

  Linking /usr/local/Cellar/opencv/2.4.8.2... 251 symlinks created

  The problem is this now seems to have broken my working project. When I try to run the project now I get the following errors
  Unfortunately after trying to rebuild the project I cannot get the error below to show up in the terminal again but it said the following error, was expected in /usr/local/include but not found in the build directory (afraid I cannot be sure of the exact wording)

  dyld: lazy symbol binding failed:

  In QT creator however, when trying to build the project it says

  error: symbol(s) not found for architecture x86_64
  
  error: linker command failed with exit code 1 (use -v to see invocation)

  Any suggestions for a fix, and also how I can get VideoWriter to work with opencv on Mac OSX after I have my project working again ?

• broadcast live video from android with ffmpeg source code

  8 novembre 2012, par keven

  Any suggestion for live stream for android.

  In my app i need to broadcast live video from android on a web,some app like Qik, Justin.tv, Ustream.tv and Bambuser.
  it is developed under ffmpeg,
  anyone would help if there is any open source project like this,or anyone had already done it
  please tell me the project name or send me a copy of the code.

  Email:liangyingshuang@gmail.com

  Thanks.

• Seeking to video frame of h264 codec in mp4 container with FFmpeg. Packet pts is always 0

  28 avril 2015, par Maxito

  I’m trying to seek to the nearest keyframe of a specific frame with FFmpeg but whenever I obtain the next frame with av_read_frame after seeking, the packet pts or dts are always 0. This only happens with h264/mp4 videos as it works correctly for some codecs in .avi container.

  I have tried using avformat_seek_file and av_seek_frame but they give me the same result.

  I also read that I shouldn’t be reading timestamps from the packet, so I tried decoding the packet first with avcodec_decode_video2 and reading AVFrame->pts information but this value is always invalid for h264/mp4 videos.

  This is the relevant code of what I’m trying to do :

  /*Relevant from header*/
  
  AVCodecContext pCodecCtx;
  
  AVFormatContext *pFormatCtx;
  
  int videoStreamIndex;
  
  
  
  int Class::getFrame(int desiredFrame, bool seek)
  
  if(seek)
  
  {
  
      /* We seek to the selected frame */
  
      if(avformat_seek_file(pFormatCtx, videoStreamIndex, 0, desiredFrame, desiredFrame, AVSEEK_FLAG_BACKWARD) < 0)
  
      //if(av_seek_frame(pFormatCtx, mVideoStream, desiredFrame, AVSEEK_FLAG_BACKWARD) < 0)
  
      {
  
      // error management
  
      }
  
      avcodec_flush_buffers(pCodecCtx);
  
  }
  
  
  
  AVPacket packet;
  
  int frameFinished;
  
  /* Loop until we find the next video frame */
  
  while(av_read_frame(pFormatCtx, &packet) >= 0 )
  
  {
  
      if(packet.stream_index == videoStreamIndex)
  
      {
  
          avcodec_decode_video2(pCodecCtx, pFrame, &frameFinished, &packet);
  
          int pcktPts;
  
  
  
          /*** management of other codecs here using av_frame_get_best_effort_timestamp() ***/
  
  
  
  
  
          /* With this approach I have been getting correct pts info after many av_read_frame loops */
  
          if(pCodecCtx->codec->id == AV_CODEC_ID_H264 && videoPath.toLower().endsWith(".mp4"))
  
          {
  
              pcktPts = av_rescale_q(packet.pts, //pFrame->pts always invalid here
  
                                        pFormatCtx->streams[videoStreamIndex]->time_base,
  
                                        pFormatCtx->streams[videoStreamIndex]->codec->time_base);
  
              pcktPts = (pcktPts/pCodecCtx->ticks_per_frame);
  
          }
  
  
  
          if(pcktPts == desiredFrame) ....
  
          /* more irrelevant code for reading, converting frame, etc */

  Perhaps I’m dealing with this kind of codec incorrectly, any idea will be highly appreciated.

  As a note, I am only interested in video frames.