OpenCV how to interrupt video record with thread

asked 2018-07-23 04:33:03 -0600

whdt gravatar image

updated 2018-07-30 06:32:53 -0600

Eduardo gravatar image

Hi everyone: i facing a problem on interrupt video while hit timestamp. with the following code below it only generate 1 second video per time. i want to make it generate the video by 30 seconds every time. please help me thank you.

for (int ix = 30; ix >= 0 ; --ix)
{
   if (!cap.read(Source))
    {
       cerr << "ERROR! blank frame grabbed\n";
       break;
     }

     vWrite.write(Source);
}
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for (int ix = 900; ix >= 0 ; --ix)

LBerger gravatar imageLBerger ( 2018-07-23 04:51:29 -0600 )edit

thanks for quick response, how to make it exactly 30 seconds , it finish recording video at 45 seconds.

whdt gravatar imagewhdt ( 2018-07-23 19:46:43 -0600 )edit

is it a way using lamba to do it?

thread timer([] () {
   this_thread::sleep_for(chrono::seconds(30));
   vwrite.write(Source);
});

i have try the code above but it don't seen like working properly because i already have a thread running for capture stream to avoid the stream disconnected and reconnect back.

whdt gravatar imagewhdt ( 2018-07-23 20:00:09 -0600 )edit

You have to use a timer. Now recording a video 30 swith frame rate equal to 30 you will need 900 images. Video time is not always real time

LBerger gravatar imageLBerger ( 2018-07-23 23:59:53 -0600 )edit

is it possible to make it real time? i test it in 1 minutes it records for 1 minutes 45 seconds.

whdt gravatar imagewhdt ( 2018-07-24 00:04:41 -0600 )edit

You will need to grab 30 frame per second then you have to check time in grab loop : grab frame at t=0 , 1/30, 2/30... and 899/30

LBerger gravatar imageLBerger ( 2018-07-24 00:16:57 -0600 )edit

i have use the code below to check the frame

capture.get(CV_CAP_PROP_POS_FRAMES)

it will show totally frame in loop grab per time start from 0 to 29 frames. sorry i don't understand how to grab frame at t = 0, 1/30, 2/30.....and 899/30 can you give me an example? thank you.

whdt gravatar imagewhdt ( 2018-07-24 00:51:27 -0600 )edit

In cap.read(Source) what is source ? a video file ? a webcam ?

LBerger gravatar imageLBerger ( 2018-07-24 01:51:26 -0600 )edit

source = get stream from webcam

whdt gravatar imagewhdt ( 2018-07-24 02:10:00 -0600 )edit

You have to check time if it is a webcam

LBerger gravatar imageLBerger ( 2018-07-24 02:32:04 -0600 )edit

thanks for suggestion

whdt gravatar imagewhdt ( 2018-07-24 02:38:12 -0600 )edit

You have to understand : when you grab from a webcam you take a picture at t=t0. If you wait 5 minutes then take a new picture you will grab what it is in front the webcam at t=t0+5 minutes not t0+pos_frame)

LBerger gravatar imageLBerger ( 2018-07-24 02:43:35 -0600 )edit

but it will face problem if webcam disconnected during calculate time need some process to reset the time because thread will reconnect back the webcam while webcam is disconnected.

whdt gravatar imagewhdt ( 2018-07-24 04:58:35 -0600 )edit
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