Skip frames and seek to end of RTSP stream

asked 2018-08-10 03:27:29 -0600

MLu
1 ●1 ●1

I capture and process an IP camera RTSP stream in a OpenCV 3.4.2 on Raspberry Pi. Unfortunately the processing takes quite a lot of time, roughly 0.2s per frame, and the stream quickly gets delayed.

I don't mind if I skip some frames so I'm looking for a way to seek to the end of the stream before capturing and processing the next frame.

vcap = cv2.VideoCapture("rtsp://{IPcam}/12")

while(1):
    ret, frame = vcap.read()
    time.sleep(0.2)              # <= Simulate processing time
    cv2.imshow('VIDEO', frame)
    if cv2.waitKey(1) == 27:
        break
    vcap.seek_to_end()           # <== How to do this?

How can I do that vcap.seek_to_end() to catch up with the stream, discard the missed frames, and start processing the most current one?

Thanks!

answered 2018-08-10 03:48:04 -0600

berak
32993 ●7 ●81 ●312

an ip stream has no "end". and you can't "seek" anything there. itdoes not know the future and does not remember the past.

but vcap.read() is actually a combination of grab() and retrieve() . so you should:

grab() as often as you can. after say, 5 frames you have reached the latest img, probably.
retrieve() and process the img only, when desired (e.g. if you're sure, you have the latest)

vcap = cv2.VideoCapture("rtsp://{IPcam}/12")
ct = 0
while(1):
    ct += 1
    ret = vcap.grab()
    if ct % 5 == 0: # skip some frames
        ret, frame = vcap.retrieve()
        if not ret: break
        time.sleep(0.2)              # <= Simulate processing time
        cv2.imshow('VIDEO', frame)
    if cv2.waitKey(1) == 27:
        break

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Comments

This really has solved the issue. Thanks a ton. (Created this forum account just to mark your reply as right answer, but can't being a newbie here :P)

Pandian ( 2020-05-22 21:55:15 -0600 )edit

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