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• How does the moov atom corrupt when editing metadata

  20 juin 2015, par Sam

  I have been editing metadata for some video files that I have, using a program called iDentify (on a mac). This is an old version of the program, made before they charged for it. It generally works perfectly, however about one in a hundred files that it processes, corrupts as it updates the metadata (artwork, description etc). The file is then un-openable.

  If I run the corrupt mp4 file through ffmpeg, I get an error saying that the moov atom could not be found. I have tried to research and I think the moov atom is sort of like a folder within the file, that holds the movie data... But I really am not sure about it. It seems like this is an issue that is normally seen when a camera crashes while filming, before it can make an index for the file. Thats not the case here, the file worked fine before running it through identify.

  What I would like to know is how editing the metadata can corrupt a file like this. Does anyone have any suggestions what the identify application would be doing to a file to corrupt it in this way ? The application is really quick (a couple of seconds), there is no encoding or new files, just inserting metadata.

  I managed to get another copy of the original good file and made a few copies of it. Every time I ran that particular video through identify, it would come out corrupted (but was absolutely fine beforehand). Therefore there must be a characteristic in the file that makes inserting metadata dangerous, causing corruption.

  Can anyone suggest what might be causing this corruption of the moov atom ? And then it might be possible to work out a fix...?

• Create GIF from MP4 with PHP

  6 janvier 2016, par senty

  I first started with installing FFMpeg and ImageMagick on my local server (while ssh'd).

  I made some research, and thought that I can achieve Mp4->GIF with first, converting mp4 -> png and then, png -> gif.

  So I tried running
  ffmpeg -i input.mp4 -r 10 man/output%05d.png. It created PNGs from Mp4 successfully. Then I tried running this php on localserver..

  $ php convertDoc.php

  $animatedGif = new Imagick();
  
  
  
  $path = "./man/";
  
  
  
  $files = scandir($path);
  
  
  
  for($i=2;$i<6;$i++) {
  
      $image = new Imagick();
  
      var_dump($files);
  
      $image->readImage($path.$files[$i]);
  
  
  
      $animatedGif->addImage($image);
  
  }
  
  
  
  $animatedGif->writeImages('testOutput.gif', true);

  But I started getting error :

  PHP Fatal error : Uncaught exception ’ImagickException’ with message ’no decode delegate for this image format

  ---

  I checked convert -list configure. I have DELEGATES bzlib mpeg fontconfig freetype jbig jng jpeg lzma png ps tiff wmf x xml zlib

  Also I checked identify -list format. I have PNG* rw- Portable Network Graphics (libpng 1.2.50) AND GIF* rw+ CompuServe graphics interchange format

  ---

  What am I doing wrong ? Am I on the right way or completely out of track ?

  What is the most optimal way of generating GIFs from MP4 in PHP either using FFMpeg or Imagick, or both ?

• Why multithead use more cpu than single for the same task of deocoing H.264 video ?

  29 juillet 2018, par gary

  I am developing an PC hardware accelerated video decoder for decoding real time H264 Annex B stream. After a bit research, I have done this job by ffmpeg. However, I try to decople the decoding process and show process, the cpu bumped.

  What I want to do is to acceleratly decode a living H.264 stream to yuv, and convert YUV to BGR for cv::Mat without display.

  I can acceleratly decode the h.264 by ffmpeg with decoder h264_qsv, the cpu usage decrease 15% indeed. Then I try to do another thing that put then CV::Mat to std::queue and read the Mat from another queue which just read with do anything else. But the cpu bumped to 30%.

  At first, I think the std::mutex accessed frequently made the performance worse, I try to use a bool flag as lock, but it seems does not work.

  How can I approach ? I have no idear why mulithread make the cpu usage increase. Is there any helpful resources to get clear intuition ?

  frame enqueue

     av_frame_q_lock.lock();
  
     if (av_frame_q.size() == MAX_QUEUE_SIZE) {
  
          av_frame_q.pop();
  
      }
  
      av_frame_q.push(cvframe);
  
      av_frame_q_lock.unlock();

  frame dequeue

      hwrtsp_open("rtsp://admin:123@10.20.37.185/cam/realmonitor?channel=1&subtype=0", "h264_qsv");
  
  cv::Mat frame;
  
  while (true) {
  
      int ret = hwrtsp_read(frame);
  
      if (ret == 0) {
  
      }
  
      cv::waitKey(40);
  
  }

  Thanks in advance !