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• whats the difference between “&” and multiple terminals in Linux Multiprocessing [closed]

  11 mai 2022, par Ma XIaoyu

  I am using Linux for multi-task processing. Specifically, calling ffmpeg multiple times to transcoding multi source videos.

  


  Strangely, when I am using :
“
ffmpeg-cmds01 &
ffmpeg-cmds02 &
ffmpeg-cmds03 &
……
”
The ffmpeg process often get errors and stop after a few hours.

  


  However, if I open several terminals and using each terminal for only one ffmpeg cmd( i.e., terminal#1 only run ffmpeg-cmd01 ; ternimal#2 only for ffmpeg-cmd02, etc.) The transcoding procedure can last for dozens of days and no errors are reported.

  


  Could anyone kindly help us to analysis what’s there differences ? Opening multiple terminals is too difficult for managing especially when the number of video streams are up to 300+.

  


  Thanks a lot for help !

  


• Fix a .WAV header

  28 décembre 2018, par Mattia Mura

  A Ransomware crypted all my files a little time ago, I started studying a way to come over that and I discovered that the ransomware only changes the code of each files up until Offset no.100000. This helped me recovering many of my files just copying and pasting those code lines on the corrupted files from other files with a similiar .ext that werent’t damaged. It has been easy with huge video files and also with some audio files like .3gp or .mp3, but I’m having big issues with a .wav file of 152 MB containing some important audio from an interview.

  I am using HxD to manipulate the code and ffmpeg to fix some of the parts of my files after this copy/paste process. I’ve already tried to fix everything with vlc but it gave me no results

  HERE is the beginning of the file, that doesn’t have any ordinary .wav header anymore because of the encryption.

  And HERE you can see the difference between offset FFFF0 and 100000, to give you a clearer idea.

  Basically I should change the code of the file up until the Offset number 100000, or anyway I should make it work despite those crypted lines. Do you know any way to solve this issue ? Thanks a lot and be patient, is my first question here !

• I need a compact c/c++ code for motion vectors extraction from mp4 file without frame decoding [on hold]

  23 mars 2018, par Andyrey

  I have searched a lot of answers on this kind of question. Many of them point out to code, presuming frame decoding :

  DCT coefficient and motion vector extraction in encoded domain ;
  https://github.com/vadimkantorov/mpegflow ;
  https://github.com/FFmpeg/FFmpeg/blob/master/doc/examples/extract_mvs.c.

  I implemented these codes in my program and saw they decode video frames, and then use frame side data for extracting motion vectors.

  Others give command lines for executing bynaries :

  Motion Vector extraction from encoded video file

  or just gives reference to huge set of library files with no idea what to do with them.

  What I badly need : code for extracting motion vectors from mp4 with no frame decoding (no pixel domain restoring). Is it possible ?

  From my 3rd reference I used code like next, where I suspect frame decoding happens :

  while (ret >= 0)
  
  {
  
      ret = avcodec_receive_frame(video_dec_ctx, frame);
  
     /*I omit some exclusion processing*/
  
      if (ret >= 0)
  
      {
  
          int i;
  
          AVFrameSideData *sd;
  
          video_frame_count++;
  
          sd = av_frame_get_side_data(frame, AV_FRAME_DATA_MOTION_VECTORS);
  
          if (sd)
  
          {
  
              const AVMotionVector *mvs = (const AVMotionVector *)sd->data;
  
              for (i = 0; i < sd->size / sizeof(*mvs); i++)
  
              {
  
                  const AVMotionVector *mv = &mvs[i];
  
                  printf("%d,%2d,%2d,%2d,%4d,%4d,%4d,%4d,0x%"PRIx64"\n",
  
                  video_frame_count, mv->source,
  
                  mv->w, mv->h, mv->src_x, mv->src_y,
  
                  mv->dst_x, mv->dst_y, mv->flags);
  
              }
  
          } 
  
          av_frame_unref(frame);
  
      }
  
  }