[open] how to define media_player_vlc (set video width/height + set loop)

Comments

• sebastiaan

  January 2014 edited 9:18PM

  Hi Ben,

  i'm trying to show a video in the middle of the screen and (at the same time) show text at the bottom of the screen. therefore i tried to set video width/height.

  If you want to do (relatively) complex things with video, such as custom scaling and drawing additional things on top of the video surface, you're probably best of writing a custom script with opencv. This is not as difficult as it sounds, and a working example is provided here:

  • http://osdoc.cogsci.nl/usage/video/#opencv

  another question is to loop a video until keyresponse.

  If you are using an inline script anyway, than this too would probably be best handled through a loop in your script.

  If you are not familiar with Python, quite a few excellent tutorials are available:

  • http://osdoc.cogsci.nl/python/about/#learningpython

  Cheers and good luck!
  Sebastiaan

  
  
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• berlin

  January 2014 edited 9:18PM

  thanks!

  i downloded the opencv-package at opencv.org but the debugger says: "ImportError: No module named cv"

  copying the opencv-folder into opensesame-plugin-folder couldnt fix the problem...

  unfortunatly the link on your "video playback" section to opencv is broken for a while (http://opencv.willowgarage.com/documentation/python/index.html)

  do you have a hint for me?

  cheers,

  ben
• sebastiaan

  January 2014 edited January 2014

  Hi Boris,

  Basically, the example is a bit outdated. It uses cv, whereas the current module (and the one supplied with OpenSesame) is cv2, for OpenCV 2.

  The script below shows how to show how to play back a video using cv2. As you can see, it's actually a bit simpler than with cv. Note that this requires the legacy back-end.

  And thanks for pointing out the broken link.

  Cheers!
  Sebastiaan

  Update: Fixed error in script

  import cv2
  import numpy
  import pygame
  # Full path to the video file
  path = exp.get_file('myvideo.avi')
  # Open the video and determine the video dimensions
  video = cv2.VideoCapture(video)
  # A loop to play the video file. This can also be a while loop until a key
  # is pressed. etc.
  for i in range(100):
      # Get a frame
      retval, frame = video.read()
      # Rotate it, because for some reason it otherwise appears flipped.
      frame = numpy.rot90(frame)
      # The video uses BGR colors and PyGame needs RGB
      frame = cv2.cvtColor(frame, cv2.COLOR_BGR2RGB)
      # Create a PyGame surface
      surf = pygame.surfarray.make_surface(frame)
      # Now you can draw whatever you want onto the PyGame surface!
      pygame.draw.rect(surf, (255,0,0), (100, 100, 200, 200))
      # Show the PyGame surface!
      exp.surface.blit(surf, (0, 0))
      pygame.display.flip()
  

  
  
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• berlin

  January 2014 edited January 2014

  thanks! unfortunatly another problem occurred:

  File "dist\numpy\lib\twodim_base.py", line 157, in rot90
  Python traceback:
  ValueError: Input must >= 2-d.
  

  ???

  i don`t want to make any changes in "twodim_base.py" or do i have to?

  cheers,

  ben
• sebastiaan

  January 2014 edited 9:18PM

  Ow right, I see. The script didn't specify which file should be read. Basically, this ...

  video = cv2.VideoCapture()
  

  ... should be ...

  video = cv2.VideoCapture(path)
  

  
  
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• berlin

  January 2014 edited January 2014

  ah ok! makes sense! but heres another debug-message:

  AttributeError: 'experiment' object has no attribute 'surface'
  

  i couldnt fix the line:

  # Show the PyGame surface!
  exp.surface.blit(surf, (0, 0))
  pygame.display.flip()
  

  damn, i have no clue of python...sorry!
• sebastiaan

  January 2014 edited 9:18PM

  Hi Ben,

  To make this script work (as I already wrote above!), you need to use the legacy back-end, or the xpyriment back-end with 'Use OpenGL' set to 'no' under back-end settings. The reason is that this script uses certain PyGame functionality that is incompatible with an OpenGL-based method of display presentation.

  Cheers!
  Sebastiaan

  
  
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• berlin

  January 2014 edited 9:18PM

  I already used the xpyriment back-end with 'Use OpenGL' set to 'no'.

  After switching to legacy back-end the video plays Didn't knew that just one of these two options works.

  now i tried to let the video play in a while loop until keypress...no success

  sorry, i am into from php-programming but its hard for me to understand the python logic...

  thanks,

  ben
• sebastiaan

  January 2014 edited 9:18PM

  Hi Ben,

  If you are not familiar with Python, there are a lot of good free tutorials to get you started. For most things, you won't need any deep Python knowledge, so don't worry. But some knowledge will be necessary if you want to do semi-complicated things with video presentation.

  • http://osdoc.cogsci.nl/python/about/#learningpython
  • http://www.codecademy.com/tracks/python

  To get you started, below is an example of how you can probe the keyboard and break the video loop when a key is pressed. For more information, see:

  • http://osdoc.cogsci.nl/python/keyboard/

  And indeed, the script didn't work with the xpyriment back-end. I added a small check to fix this, it's just a matter of selecting the right 'surface'.

  Cheers!
  Sebastiaan

  import cv2
  import numpy
  import pygame
  from openexp.keyboard import keyboard
  # Create a keyboard object
  my_keyboard = keyboard(exp, timeout=0)
  # Get the PyGame surface in a way that works for the legacy back-end, as well as
  # the xpyriment back-end with 'Use OpenGL' set to 'no'.
  if self.get('canvas_backend') == 'legacy':
      surface = exp.surface
  elif self.get('canvas_backend') == 'xpyriment':
      surface = exp.window
  else:
      raise Exception('This script requires legacy or xpyriment (no opengl)')
  # Full path to the video file
  path = exp.get_file('myvideo.avi')
  # Open the video and determine the video dimensions
  video = cv2.VideoCapture(path)
  # A loop to play the video file. This can also be a while loop until a key
  # is pressed. etc.
  while True:
      # Get a frame and break the loop if we failed, usually because the video
      # ended.
      success, frame = video.read()
      if not success:
          break
      # Rotate it, because for some reason it otherwise appears flipped.
      frame = numpy.rot90(frame)
      # The video uses BGR colors and PyGame needs RGB
      frame = cv2.cvtColor(frame, cv2.COLOR_BGR2RGB)
      # Create a PyGame surface
      surf = pygame.surfarray.make_surface(frame)
      # Now you can draw whatever you want onto the PyGame surface!
      pygame.draw.rect(surf, (255,0,0), (100, 100, 200, 200))
      # Show the PyGame surface!
      surface.blit(surf, (0, 0))
      pygame.display.flip()
      # Poll the keyboard and break the loop if a key was returned.
      key, time = my_keyboard.get_key()
      if key != None:
          break
  

  
  
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• berlin

  February 2014 edited February 2014

  the video was flipped in left/right direction so i had to add fliplr before rot90:

  frame = numpy.fliplr(frame)
  frame = numpy.rot90(frame)
  

  some further questions:

  • the video plays about 2times faster as normal? sample-frequence in back-end-settings and video sample-frequence are equal.

  • there is no sound?

  any ideas? thanks, ben
• sebastiaan

  February 2014 edited February 2014

  the video was flipped in left/right direction so i had to add fliplr before rot90:

  Yes that might be, I think it depends on the format. Just flip and rotate until it looks right!

  the video plays about 2times faster as normal? sample-frequence in back-end-settings and video sample-frequence are equal.

  You need to determine the framerate yourself in this script. So if it's too fast, just add a self.sleep() somewhere in the loop.

  there is no sound?

  Right, this is video only. Perhaps you misunderstood the script, so just to avoid confusion: It retrieves image frames from the video file and puts them on the screen. That's all, it's really very basic. It's not a real video engine that controls the framerate or handles audio.

  
  
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• refuzee

  March 2015 edited 9:18PM

  what if it plays to slow ?
• sebastiaan

  March 2015 edited 9:18PM

  what if it plays to slow ?

  That's possible, because there's quite a bit of processing going on, and not in a very optimized way. I'm afraid the only real solution would be to use a lower resolution video. (Or think of a more efficient script that does the same thing, but that might not be trivial.)

  
  
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