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• Saving the openGL context as a video output

  16 septembre 2016, par activatedgeek

  I am currently trying to save the animation made in openGL to a video file. I have tried using openCV’s videowriter but to no advantage. I have successfully been able to generate a snapshot and save it as bmp using the SDL library. If I save all snapshots and then generate the video using ffmpeg, that is like collecting 4 GB worth of images. Not practical.
  How can I write video frames directly during rendering ?
  Here the code i use to take snapshots when I require :

  void snapshot(){
  
  SDL_Surface* snap = SDL_CreateRGBSurface(SDL_SWSURFACE,WIDTH,HEIGHT,24, 0x000000FF, 0x0000FF00, 0x00FF0000, 0);
  
  char * pixels = new char [3 *WIDTH * HEIGHT];
  
  glReadPixels(0, 0,WIDTH, HEIGHT, GL_RGB, GL_UNSIGNED_BYTE, pixels);
  
  
  
  for (int i = 0 ; i <height>pixels) + snap->pitch * i, pixels + 3 * WIDTH * (HEIGHT-i - 1), WIDTH*3 );
  
  
  
  delete [] pixels;
  
  SDL_SaveBMP(snap, "snapshot.bmp");
  
  SDL_FreeSurface(snap);
  
  }
  
  </height>

  I need the video output. I have discovered that ffmpeg can be used to create videos from C++ code but have not been able to figure out the process. Please help !

  EDIT : I have tried using openCV CvVideoWriter class but the program crashes ("segmentation fault") the moment it is declared.Compilation shows no errors ofcourse. Any suggestions to that ?

  SOLUTION FOR PYTHON USERS (Requires Python2.7,python-imaging,python-opengl,python-opencv, codecs of format you want to write to, I am on Ubuntu 14.04 64-bit) :

  def snap():
  
      pixels=[]
  
      screenshot = glReadPixels(0,0,W,H,GL_RGBA,GL_UNSIGNED_BYTE)
  
      snapshot = Image.frombuffer("RGBA",W,H),screenshot,"raw","RGBA",0,0)
  
      snapshot.save(os.path.dirname(videoPath) + "/temp.jpg")
  
      load = cv2.cv.LoadImage(os.path.dirname(videoPath) + "/temp.jpg")
  
      cv2.cv.WriteFrame(videoWriter,load)

  Here W and H are the window dimensions (width,height). What is happening is I am using PIL to convert the raw pixels read from the glReadPixels command into a JPEG image. I am loading that JPEG into the openCV image and writing to the videowriter. I was having certain issues by directly using the PIL image into the videowriter (which would save millions of clock cycles of I/O), but right now I am not working on that. Image is a PIL module cv2 is a python-opencv module.

• ffmpeg decompilation of image frames producing images of much more size

  7 octobre 2013, par user2007454

  I have extracted image frames using ffmpeg from a video(video a) deleted alternate frames and applied compression on the remaining frames and again made a video (video b) ffmpeg -i "input_file%d.png" "outputfile.3gp" my question here is ideally the size of video b should be much lesser than video a as it contains lesser number of frames those are also the compressed one but to my utter surprise video b is much larger in size from video a, to have a check I have extracted the frames from video b the frames are way larger in size around 10 times the original size, if anybody can help me out or explain such behavior from ffmpeg library and how we could control such behavior, thanks in advance.

• FFMPEG installation & configuration with xampp on fedora

  10 octobre 2013, par UMI

  I have running Fedora 8, where I have installed XAMPP-Linux. First I installed latest version with Xampp-Linux-1.8.3 including PHP 5.5 from "http://www.apachefriends.org/en/xampp-linux.html".

  After setting up everything, tried to install "FFMPEG" from "http://www.nixgurus.com/fedora/installing-ffmpeg-using-yum-on-centos-redhat-fedora/". This is the only guide which gets completed with successful installation and configuration, otherwise all other tried tutorials got leave me middle of nowhere.

  Note : While installing FFMPEG following above provided URL, "phpize" did not work to me so I had to install php-devel by running "yum install php-devel" command. I always got different "Zend Module" and "Zend Extension API" versions.

  When I installed ffmpeg and put extension in "php.ini" with correct path, it never appeared in phpinfo().

  Then after searching, I got a hint that installed "FFMPEG" will not be compatible to the installed PHP version. So I removed complete pack of XAMMP-LINUX and installed old one with Xampp-Linux-1.8.2 including PHP 5.4. But it result were same.

  Then, I decided to use more older version and it was Xampp-Linux-1.8.1 including PHP 5.4. Now currently I have this version but having version results are totally changed that after installation of FFMPEG when I put ffmpeg.so with its correct path in PHP.INI (definitely restart the server on every change) server behaves strange way that PHP files get downloaded by browsers and when I comment same line and restart web server everything works well.

  Just to let you know that, even I have given path "extension=/usr/lib/php/modules/ffmpeg.so" which did not work and even moved files to default extension path "/opt/lampp/lib/php/extensions/no-debug-non-zts-20100525" as well but in vain.

  Looking forward to your help please.