Opencv videocapture with multiple files in scanned directory

Python Help
1

Hi all,

I’m kinda stuck on this and can’t figure out what’s going on. What I would like to do is:

  • scan a directory for video (mp4) files
  • open each file for processing with opencv videocapture
# file operations
import os
# Motion detection
import cv2


# Scan target directory
# os.scandir returns an iterator, make it a list to be re-usable

# Target directory is in the same directory as the script
targetDirectory = "videofiles"
dircontent = list(os.scandir(targetDirectory))

# Search for mp4 files and make a list [ [filename, path], [filename, path], ... ]
mp4Files = [[f.name[:-4], os.path.abspath(f.name)] for f in dircontent if f.name.lower().endswith('.mp4')]

for videofile in mp4Files:

    print(videofile[1], " -- ", type(videofile[1]))
    # This print: E:\Projects\Programming\Python\OpenCV\_CaptureSaveROI\Motiondetection_Batch_Heatmap\Burglary.mp4  --  <class 'str'>

    # Open file to process
    cap = cv2.VideoCapture(videofile[1])

    print(cap)
    # This prints: <VideoCapture 018CB4C0>

    # the following doesn't give an error:
    # cap = cv2.VideoCapture("E:/Projects/Programming/Python/OpenCV/_CaptureSaveROI/Motiondetection_Batch_Heatmap/videofiles/Burglary.mp4")

    ret, frame1 = cap.read()
    heatmap = frame1.copy() # <<<<<<< ERROR

The error I get is:

heatmap = frame1.copy()
AttributeError: 'NoneType' object has no attribute 'copy'

Is there anyone who knows what’s going on here?
Thanks in advance

2

I just tried this:

for videofile in mp4Files:

    print(videofile[1], " -- ", type(videofile[1]))
    # This print: E:\Projects\Programming\Python\OpenCV\_CaptureSaveROI\Motiondetection_Batch_Heatmap\Burglary.mp4  --  <class 'str'>

    # Open file to process
    cap = cv2.VideoCapture(videofile[1])

    # the following doesn't give an error:
    # cap = cv2.VideoCapture("E:/Projects/Programming/Python/OpenCV/_CaptureSaveROI/Motiondetection_Batch_Heatmap/videofiles/Burglary.mp4")

    print(cap)
    # This prints: <VideoCapture 018CB4C0>

    if (cap.isOpened() == False):
        print("Error opening the video file")
    else:
        ret, frame1 = cap.read()
        heatmap = frame1.copy() # <<<<<<< ERROR

The output is:

E:\Projects\Programming\Python\OpenCV\_CaptureSaveROI\Motiondetection_Batch_Heatmap\Burglary.mp4  --  <class 'str'>
<VideoCapture 00C7B4C0>
Error opening the video file

I’m scratching my head over this one…

3

Howdy Bart,

The second element of the tuple returned by cap.read(), which is assigned to frame1, seems to be ‘None’. Does that answer your question?

Cheers, Dominik

4

maybe this helps:

?

Cheers, Dominik

5

The thing is that the cap object is not valid when using a (string) videofilepath coming from the list.

ret, frame1 = cap.read()
    print(ret)                  # returns false
    heatmap = frame1.copy()     # <<<<<<< ERROR: 'NoneType' object has no attribute 'copy'

ret returns false and frame1 doesnt exist (is nonetype) So yeah that a problem

cap.isOpened() returns true if I feed the literal string into cv2.VideoCapture() If I input the string from the list to cv2.VideoCapture() I get the nonetype error.

6

I’ve been staring at this too long and missed the difference in the paths:

…Motiondetection_Batch_Heatmap\Burglary.mp4
…Motiondetection_Batch_Heatmap/videofiles/Burglary.mp4

Changing
os.path.abspath(f.name)
to
os.path.abspath(f)

did the trick.

Problem solved

1 Like