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My task today was to practice recording video with cv2.videoWriter(). Using code I pieced together from some of Adrian Rosenbrock’s tutorials and Dr. Mitchell’s stoplighttracker.py I created the following code:

#https://www.pyimagesearch.com/2015/03/30/accessing-the-raspberry-pi-camera-with-opencv-and-python/
#https://www.pyimagesearch.com/2016/02/22/writing-to-video-with-opencv/
# import the necessary packages
from picamera.array import PiRGBArray
from picamera import PiCamera
import time
import datetime
import cv2
from imutils.video import VideoStream

# initialize the camera and grab a reference to the raw camera capture
camera = PiCamera()
camera.resolution = (1920, 1088)
camera.framerate = 32
rawCapture = PiRGBArray(camera, size=(1920, 1088))

#Define the codec
today = time.strftime("%Y%m%d-%H%M%S")
fps_out = 32
fourcc = cv2.VideoWriter_fourcc(*'XVID')
out = cv2.VideoWriter(today + ".avi", fourcc, fps_out, (1920, 1088))

# allow the camera to warmup
time.sleep(0.1)
# capture frames from the camera
for frame in camera.capture_continuous(rawCapture, format="bgr", use_video_port=True):
    # grab the raw NumPy array representing the image, then initialize the timestamp
    # and occupied/unoccupied text
    image = frame.array
    # show the frame
    cv2.imshow("Frame", image)
    key = cv2.waitKey(1) & 0xFF

    #save the frame to a file
    out.write(image)

    # clear the stream in preparation for the next frame
    rawCapture.truncate(0)
    # if the `q` key was pressed, break from the loop
    if key == ord("q"):
        break

The camera.resolution, out resolution, and rawCapture have to have the same dimensions or the video won’t export.

I ran into an interesting phenomenon where the exported video is significantly shorter than the recorded video. I suspect this has something to do with a mismatch in frame rates. The video plays back at a much higher frame rate than I recorded.

fourcc = cv2.VideoWriter_fourcc(*’MJPG’)

fps_out = 10

out = cv2.VideoWriter(today + “.avi”, fourcc, fps_out, (1920, 1088))

I tried again.

Same results.

What if I exported a higher frame rate? (32 fps)

That’s actually faster.

What about trying XVID instead of MJPG?

Wow time flies when we’re having fun

I’ll have to do some more digging to figure out how to resolve this issue.