Recherche avancée

Sur d’autres sites (5848)

• Python : What's the fastest way to load a video file into memory ?

  8 juillet 2017, par michaelh

  First some background

  I am trying to write my own set of tools for video analysis, mainly for detecting render errors like flashing frames and possibly some other stuff in the future.

  The (obvious) goal is to write a script, that is faster and more accurate than me watching the file in real time.

  Using OpenCV, I have something that looks like this :

  import cv2
  
  
  
  
  
  vid = cv2.VideoCapture("Video/OpenCV_Testfile.mov", cv2.CAP_FFMPEG)
  
  width = 1024
  
  height = 576
  
  length = vid.get(cv2.CAP_PROP_FRAME_COUNT)
  
  
  
  for f in range(length):
  
      blue_values = []
  
      vid.set(cv2.CAP_PROP_POS_FRAMES, f)
  
      is_read, frame = vid.read()
  
      if is_read:
  
          for row in range(height):
  
              for col in range(width):
  
                  blue_values.append(frame[row][col][0])
  
      print(blue_values)
  
  vid.release()

  This just prints out a list of all blue values of every frame.
   Just for simplicity (My actual script compares a few values across each frame and only saves the frame number when all are equal)

  Although this works, it is not a very fast operation. (Nested loops, but most important, the read() method has to be called for every frame, which is rather slow.
  I tried to use multiprocessing but basically ended up having the same crashes as described here :

  how to get frames from video in parallel using cv2 & multiprocessing in python

  I have a 20s long 1024x576@25fps Testfile which performs as follows :

  • mov, ProRes : 15s
  • mp4, h.264 : 30s (too slow)

  My machine is capable of playing back h.264 in 1920x1080@50fps with mplayer (which uses ffmpeg to decode). So, I should be able to get more out of this. Which leads me to

  my Question

  How can I decode a video and simply dump all pixel values into a list for further (possibly multithreaded) operations ? Speed is really all that matters. Note : I’m not fixated on OpenCV. Whatever works best.

  Thanks !

• lavf/qtpalette : Ignore greyscale bit in certain cases

  2 janvier 2016, par Mats Peterson

  lavf/qtpalette : Ignore greyscale bit in certain cases
  The QuickTime File Format Specification states the following :
  "Depth : A 16-bit integer that indicates the pixel depth of the
  
  compressed image. Values of 1, 2, 4, 8 ,16, 24, and 32 indicate the
  
  depth of color images. The value 32 should be used only if the image
  
  contains an alpha channel. Values of 34, 36, and 40 indicate 2-, 4-, and
  
  8-bit grayscale, respectively, for grayscale images."
  There is no mention of value 33, i.e. 1-bit video (0x01) with the
  
  greyscale bit (0x20) set. I therefore suggest that we ignore the
  
  greyscale bit when processing 1-bit video. Another reason to do this is
  
  that the first 1-bit sample file below will be displayed properly with
  
  blue colors in QuickTime in Windows or Mac *in spite of* the greyscale
  
  bit being set.
  Also, QuickTime in Windows or Mac ignores the greyscale bit if the
  
  video sample description contains a palette, regardless of bit depth.
  
  This is undocumented behaviour, but I think we should do the same, and
  
  it seems pretty logical after all, since one wouldn’t really bother
  
  putting a customized palette into a grayscale file anyway. See the
  
  second 8-bit sample file below, which has the greyscale bit set, and
  
  which contains a palette in the video sample description. In Windows or
  
  Mac, it will be displayed with the palette in the sample description, in
  
  spite of the greyscale bit being set.
  Sample file 1 (1-bit QuickTime Animation) :
  
  https://drive.google.com/open?id=0B3_pEBoLs0faTThSek1EeXQ0ZHM
  
  Earth Spin 1-bit qtrle orig.mov
  Sample file 2 (8-bit QuickTime Animation) :
  
  https://drive.google.com/open?id=0B3_pEBoLs0fad2s0V1YzUWo5aDA
  
  quiz-palette+gs.mov
  Signed-off-by : Michael Niedermayer <michael@niedermayer.cc>
  

  • [DH] libavformat/qtpalette.c

• 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.