Playing Video with OpenCV from inline_script

dalbohn

I am attempting to play a video using an inline_script following the example given [here] (http://osdoc.cogsci.nl/usage/video/#LstExampleCV2). However, despite searching the forums for some potential fixes, I still get this error when trying to play a video via the experiment.

  File "dist\numpy\lib\twodim_base.py", line 177, in rot90
 ValueError: Input must >= 2-d.

Here is the full script that I am using for play the video:

import cv2
import numpy
import pygame

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('full\path\to\video.mp4')

# Open the video and determine the video dimensions
video = cv2.VideoCapture(path)

# A loop to play the video file.
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()

Thanks,
Dan

sebastiaan

Hi Dan,

It looks like the frame object is not what it should be when it is passed to numpy.rot90(). The easiest way to debug this is simply to print out the return value and type of the frame object to the debug window:

# Get a frame
retval, frame = video.read()
print('retval: %s' % retval)
print('frame: %s' % type(frame))

For me this returns:

retval: True
frame: <type 'numpy.ndarray'>

If it returns something else, OpenCV is probably unable to read the video, which can be for any number of reasons. For example, the path can be incorrect, or the video format may not be supported.

Cheers!
Sebastiaan