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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.

• What is the correct way to calculate SSIM ?

  19 mai 2023, par jamacoe

  On Windows 10, I have installed ImageMagick, Version 7.1.1-Q16-HDRI.

  


  I have a high resolution .png image that I convert to jpg with 75% quality :

  


  magick myImage.png -quality 75 myImage.jpeg


  


  Now I want to calculate SSIM to judge the quality of the .jpeg in comparison to the original .png.

  


  First, I am using ffmpeg.exe version 4.2.3 from the very same ImageMagick installation :

  


  ffmpeg.exe -i myImage.jpeg -i myImage.png -lavfi ssim=stats_file=ssim_logfile.txt -f null -


  


  Results in ssim_logfile.txt :

  


  n:1 Y:0.959684 U:0.957603 V:0.976335 All:0.962112 (14.215018)


  


  So I assume that the SSIM value has been calculated as 0.962112

  


  Now I'll use magick to calculate the same metric :

  


  magick myImage.jpeg myImage.png -metric SSIM -compare -format "%[distortion]" info:


  


  Output is :

  


  0.925167


  


  That's a huge difference ! So I think I'm making an error here with one or the other way.

  


  What is the correct way to calculate SSIM ?

  


• avformat/movenc : fixed fmp4 packets containing incorrect flags after transcoding

  10 avril 2023, par Wang Yaqiang

  avformat/movenc : fixed fmp4 packets containing incorrect flags after transcoding
  When write multi-trun box, the MOV_TRUN_FIRST_SAMPLE_FLAGS flag
  
  need judge by first param, not 0.
  
  If the original video contains consecutive I frames,
  
  this will cause the packets of fmp4 have error sample_flags ,
  
  and then incorrect keyframes were generated,
  
  and then error packet will be seeked.
  Signed-off-by : Wang Yaqiang <wangyaqiang03@kuaishou.com>
  
  Signed-off-by : Steven Liu <liuqi05@chinaffmpeg.org>
  

  • [DH] libavformat/movenc.c