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• Executing bash shell command and extract output —> invalid file error

  29 novembre 2016, par Ingeborg

  I want to extract the framesize of a video from a file. For this purpose, I have launched an ffmpeg command via bash shell, and I want to extract the output. This command is working well in the bash shell, and returns the output as wanted.

  ffprobe -v error -count_frames -of flat=s=_ -select_streams v:0 -show_entries stream=nb_read_frames /home/peter/DA/videos/IMG-2014-1-10-10-4-37.avi

  I want to call it via C++ and read out the result. I use the IDE Qt 4.8.6 with GCC 4.8 compiler.

  For my code, I use this template :

  executing shell command with popen

  and changed it for my demands to

  #include <iostream>
  
  #include <string>
  
  #include 
  
  
  
  using namespace std;
  
  
  
  
  
  int main()
  
  {
  
     FILE* pipe = popen("echo $(ffprobe -v error -count_frames -of flat=s=_ -select_streams v:0 -show_entries stream=nb_read_frames /home/peter/DA/videos/IMG-2014-1-10-10-4-37.avi)", "r");
  
   if(!pipe)
  
   {
  
       cout &lt;&lt; "error" &lt;&lt; endl;
  
       return 1;
  
   }
  
   char* buffer = new char[512];
  
  
  
  string result;
  
  fgets(buffer, sizeof(buffer), pipe) ;
  
  while(!feof(pipe))
  
  {
  
      if(fgets(buffer, sizeof(buffer), pipe) != NULL)
  
      {
  
          cout &lt;&lt; buffer &lt;&lt; endl;
  
          result += buffer;
  
      }
  
  }
  
  pclose(pipe);
  
  cout &lt;&lt; result&lt;&lt; endl;
  
  return 0;   
  
  }
  
  </string></iostream>

  The Qt console returned me this warning, and it is rending with return 0 :

  /home/peter/DA/videos/IMG-2014-1-10-10-4-37.avi: Invalid data found when processing input

  and "pipe" is empty.

  When I compile the main.cpp file above with g++ in the shell it works nice too.

• How to change the size of audio visualisers in ffmpeg ?

  3 juillet 2017, par Meme Stream

  I have this command in ffmpeg :

  echo shell_exec("$ffmpeg  -i test.aiff -y -filter_complex '[0:a]showfreqs=s=1920x1080:mode=bar:ascale=log:fscale=lin:win_size=w1024:win_func=poisson:colors=blue,format=yuv420p[v]' -map '[v]' -map 0:a output2.mp4 2>&1");

  I want to make it so that the video dimensions are still 1080p but the showfreqs graph is squashed and located near the bottom of the screen. How do I do this ? Thanks.

• ffmpeg add alpha to the video

  3 octobre 2014, par death_relic0

  Basically I have a video with a green background, and I mean a perfect green background (red = 0, green = 255, blue = 0) and I want to convert this to alpha (i.e add an alpha channel where 0 255 0 corresponds to alpha)

  I am very new to ffmpeg so I can’t figure this out. I am guessing it has something to do with the alphamerge option.

  THanks in advance