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• Which OpenCV FOURCC codecs should I use for my Python program ?

  17 mars 2020, par Rainer H.

  I have implemented a Python script which displays a video to the user and records it. The video is saved either compressed or uncompressed.

  In an old program I have seen, that the "DIVX" MPEG-4 and the "IYUV" codecs were used. For some reason, they don’t work on my computer (OUTPUT_VIDEO is a MP4-file).

  OpenCV: FFMPEG: tag 0x58564944/'DIVX' is not supported with codec id 13 and format 'mp4 / MP4 (MPEG-4 Part 14)'
  
  OpenCV: FFMPEG: fallback to use tag 0x00000020/' ???'

  The "MPJPG" codec works with ".avi" files.

  Because I’m not sure about the codecs, I would like to ask, which codecs should I use for my script to achieve the following requirements :

  • the video sequence can be saved as .mp3, .mp4 file (both compressed) or as .avi file (uncompressed).
  • Python script should work on Windows and Linux platforms.

  This is my source code :
  main.py

  #!/usr/bin/env python
  
  # -*- coding: utf-8 -*-
  
  
  
  import os
  
  import cv2
  
  import platform
  
  
  
  #=========== TO CHANGE ===========
  
  INPUT_VIDEO = os.path.join("..", "resources", "video.mp4")
  
  OUTPUT_VIDEO = os.path.join("..", "recorded", "recorded.avi")
  
  compress = False
  
  #=========== TO CHANGE ===========
  
  
  
  WINDOW_NAME = "Video Recorder"
  
  
  
  player = cv2.VideoCapture(INPUT_VIDEO)
  
  
  
  # Get the frames per second (fps) of the video.
  
  fps = player.get(cv2.CAP_PROP_FPS)
  
  
  
  # Get width and height via the video capture property.
  
  width = player.get(cv2.CAP_PROP_FRAME_WIDTH)
  
  height = player.get(cv2.CAP_PROP_FRAME_HEIGHT)
  
  
  
  # Define the codec and create VideoWriter object according to the used operating system.
  
  four_cc = None
  
  if platform.system() == "Windows":
  
      if compress:
  
          four_cc = cv2.VideoWriter_fourcc(*"MJPG")  # *"DIVX")  # DIVX MPEG-4 codec.
  
      else:
  
          four_cc = cv2.VideoWriter_fourcc(*"MJPG")  # *"IYUV")  # Uncompressed yuv420p in avi container.
  
  elif platform.system() == "Linux":
  
      if compress:
  
          four_cc = cv2.VideoWriter_fourcc(*"DIVX")  # DIVX MPEG-4 codec.
  
      else:
  
          four_cc = cv2.VideoWriter_fourcc(*"IYUV")  # Uncompressed yuv420p in avi container.
  
  
  
  recorder = cv2.VideoWriter(OUTPUT_VIDEO, four_cc, fps, (int(width), int(height)))
  
  
  
  if player is None:
  
      quit()
  
  
  
  while player.isOpened():
  
      ret, frame = player.read()
  
  
  
      if ret:
  
          cv2.imshow(WINDOW_NAME, frame)
  
          recorder.write(frame)
  
      else:
  
          break
  
  
  
      key_code = cv2.waitKey(1)
  
  
  
      # Closes the window if the ESC key was pressed.
  
      if key_code == 27:
  
          break
  
  
  
      # Closes the window if the X button of the window was clicked.
  
      if cv2.getWindowProperty(WINDOW_NAME, 1) == -1:
  
          break
  
  
  
  player.release()
  
  recorder.release()
  
  cv2.destroyAllWindows()

  I’m using a Windows 7 computer, with opencv-contrib-python 3.4.0.12 and Python 3.6.

• How to redirect the output of an invoked program to a file ?

  26 avril 2013, par Jim Miller

  I've got some PHP code that, among other things, uses system() to call ffmpeg to encode a video. When I run this from a command line, I can redirect the output of the PHP script to a file in the usual way — php mycode.php > mycode.log — and I get not only whatever print statements I call in PHP, but also the stuff produced by ffmpeg, which I want. All's well.

  Now, however, I want to launch the PHP script in the background via a web page : I do some stuff on my site that causes this to run :

  $the_command = "/bin/php $php_file_name > $log_file_name &";
  
  $the_result = system($the_command, $retval);

  This successfully runs my script in a background PHP process, and my videos are still getting encoded by ffmpeg. However, the only thing I'm getting in my redirected log file are the print statements in the script — the output of the ffmpeg invocations are getting sent off to the ether somewhere. Is there any way I can get these saved in the log file as well ?

• Cannot Compile C Program That Uses a Library (FFmpeg) with GCC Because of the Library's Include Statements

  12 septembre 2019, par NetherGranite

  I am unable to compile a C project that uses a library called "FFmpeg" with a compiler called "GCC", and I believe it might be either because I don’t quite understand how #include works or because I am using the wrong compilation process.

  In a folder called Test, I have a file Test/test.c with the following contents :

  #include 
  
  #include 
  
  #include "FFmpeg/libavcodec/avcodec.h"

  The folder FFmpeg is located at Test/FFmpeg. When I try to compile this with GCC, I receive the following error :

  fatal error: libavutil/samplefmt.h: No such file or directory

  The file Test/FFmpeg/libavcodec/avcodec.h has the following code in it :

  #include "libavutil/samplefmt.h"
  
  #include "libavutil/attributes.h"
  
  #include "libavutil/avutil.h"
  
  ... //many more #include statements

  Is the issue here that I need to add "FFmpeg/" to all of these include statements ?

  If so, is there a way to automatically do this ? This library is enormous and probably has hundreds of these statements.

  If not, what should I be doing instead ? Should I attempt to compile the library by itself ? If so, how do I then include this compiled version of the library in my program ?

  ---

  Notes :

  • The command I am using to compile is gcc -c test.c.
  • I have GCC installed via MinGW.
  • I ultimately need to be able to compile this program to both a .dll and an .so.

  ---

  I apologize if any of the terminology I use here is incorrect or if my explanations are poor. I know almost nothing about compilation. Please let me know if I need to fill in more information.