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• Which is the better way to use ffmpeg ?

  11 mai 2016, par seaguest

  We need ffmpeg to do some video processing, like video format conversion, live stream snapshot..., we won’t go deep in ffmpeg.

  Now I am wondering what would be the better way to use ffmpeg, we are developping in Golang, either we call ffmpeg like shell command line, or we use libav* library of ffmpeg.

  command line:
  
      Pros: 
  
          easy to use, reliable (I got a quality loss problem with library mode), many tutorials
  
      Cons:
  
          the is is a separate process, out of our control, we can't get detailed information of the process, like the video conversion progressing data
  
          the command line way seems not so cool, this is not well integrated in the whole project.
  
  
  
  libav* library:
  
      Pros:
  
          we can have the process detailed data, progressing status....
  
          ...
  
  
  
      Cons:
  
          difficult to use, much less materials

  Could anyone give your idea which is the better way to use ffmpeg ?

  Before this question, I have asked another two questions :

  One is regarding calling libav* library caused the qulity loss problem :
  Why calling libav* library doesn’t have same quality as ffmpeg command line ?

  One is for command line progressing status retrieving problem :
  How to get the realtime output for a shell command in golang ?

• FATE/dnn : let fate/dnn tests depend on ffmpeg static libraries

  7 août 2019, par Guo, Yejun

  FATE/dnn : let fate/dnn tests depend on ffmpeg static libraries
  background :
  
  DNN (deep neural network) is a sub module of libavfilter, and FATE/dnn
  
  is unit test for the DNN module, one unit test for one dnn layer.
  
  The unit tests are not based on the APIs exported by libavfilter,
  
  they just directly call into the functions within DNN submodule.
  There is an issue when run the following command :
  
  build$ ../ffmpeg/configure —disable-static —enable-shared
  
  make
  
  make fate-dnn-layer-pad
  And part of error message :
  
  tests/dnn/dnn-layer-pad-test.o : In function `test_with_mode_symmetric' :
  
  /work/media/ffmpeg/build/src/tests/dnn/dnn-layer-pad-test.c:73 : undefined reference to `dnn_execute_layer_pad'
  The root cause is that function dnn_execute_layer_pad is a LOCAL symbol
  
  in libavfilter.so, and so the linker could not find it when build dnn-layer-pad-test.
  
  To check it, just run : readelf -s libavfilter/libavfilter.so | grep dnn
  So, add dependency in fate/dnn Makefile with ffmpeg static libraries.
  
  This is the same method used in fate/checkasm
  Signed-off-by : Guo, Yejun <yejun.guo@intel.com>
  
  Signed-off-by : Pedro Arthur <bygrandao@gmail.com>
  

  • [DH] tests/dnn/Makefile

• Cannot open videos in Opencv

  12 mai 2013, par Mahesh

  I am trying to open .avi file in opencv. When I run the code I do not get any error but the video does not play. I searched around and I guess it requires ffmpeg to be installed. So I installed it using
  sudo apt-get install libavformat-dev libavcodec-dev libavfilter-dev libswscale-dev
  It still does not work. Maybe the compiler needs to know where to find ffmpeg. I am using gcc compiler.
  Thanks.

  @Paul R : I have just copied the code from the Learning Opencv textbook, so wasn't including it. The code :

  #include
  
  #include
  
  int main( int argc, char** argv ) {
  
  cvNamedWindow( "Example2", CV_WINDOW_AUTOSIZE );
  
  CvCapture* capture = cvCreateFileCapture( argv[1] );
  
  IplImage* frame;
  
  while(1) {
  
      printf("Inside");
  
      frame = cvQueryFrame( capture );
  
      if( !frame ) break;
  
      cvShowImage( "Example2", frame );
  
      char c = cvWaitKey(33);
  
      if( c == 27 ) break;
  
  }
  
  cvReleaseCapture( &capture );
  
  cvDestroyWindow( "Example2" );

  }

  @praks411 :

  printf("%s",argv[1]);
  
  CvCapture* capture = cvCreateFileCapture( argv[1] );
  
  if(!capture)
  
  {   
  
          printf("failed\n");
  
      return -1; 
  
  }

  It prints the argument correctly and the capture fails.