CODEWITHSUNDEEP
pythonopencv
Miroslav Karpíšek
Miroslav Karpíšek

Reputation: 99

imshow() with desired framerate with opencv

Is there any workaround how to use cv2.imshow() with a specific framerate? Im capturing the video via VideoCapture and doing some easy postprocessing on them (both in a separeted thread, so it loads all frames in Queue and the main thread isn't slowed by the computation). I tryed to fix the framerate by calculating the time used for "reading" the image from the queue and then substract that value from number of miliseconds avalible for one frame: if I have as input video with 50FPS and i want to playback it in real-time i do 1000/50 => 20ms per frame. And then wait that time using cv2.WaitKey() But still I get some laggy output. Which is slower then the source video

Upvotes: 0

Views: 5058

Answers (2)

Hamza Chaudhary
Hamza Chaudhary

Reputation: 71

I faced the same video in one of my project in which my source video have 2 fps. so in order to show it in good manners using cv2.imshow I used a delay function before displaying of frame. Its a kind of hack but this thing work for me. The code for this hack is given below. Hope you will get some help from it. peace!

import cv2
import numpy as np
import time
cap = cv2.VideoCapture (0)

width = 400
height = 350

while True:
    ret, frame = cap.read()
    frame = cv2.resize(frame, (width, height))
    flipped = cv2.flip(frame, 1)
    framerot = cv2.rotate(frame, cv2.ROTATE_90_COUNTERCLOCKWISE)
    framerot = cv2.resize(framerot, (width, height))
    StackImg = np.hstack([frame, flipped, framerot])
    #Put time of sleep according to your fps
    time.sleep(2)
    cv2.imshow("ImageStacked", StackImg)
    if cv2.waitKey(1) & 0xff == ord('q'):
        break
cv2.destroyAllWindows()

Upvotes: 1

Ta946
Ta946

Reputation: 1412

I don't believe there is such a function in opencv but maybe you could improve your method by adding a dynamic wait time using timers? timeit.default_timer() calculate the time taken to process and subtract that from the expected framerate and maybe add a few ms buffer.

eg cv2.WaitKey((1000/50) - (time processing finished - time read started) - 10)

or you could have a more rigid timing eg script start time + frame# * 20ms - time processing finished

I haven't tried this personally so im not sure if it will actually work, also might be worth having a check so the number isnt below 1

Upvotes: 1

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