Capture video before and after a trigger

Posted on 2011-03-25
Medium Priority
Last Modified: 2013-11-13
I am looking for ideas on how to achieve the following:

1. A video camera streams feed continuously, but it is not recorded
2. An event occurs - e.g a door is opened, triggering a switch
3. The video from 30s before the event and up to 30s after the event is captured and saved to disk
4. The system waits for any subsequent events and repeats the process.

The video stream is going to be VGA standard at 25fps - any hints?
Question by:cquinn
  • 2
LVL 38

Expert Comment

ID: 35218241

There's a lot of motion detection software out there, and the state of the art is pretty good. Do you have to have a physical trigger? Because that gets a lot more complicated.

LVL 15

Author Comment

ID: 35219932
It has to be a trigger, as there will already be a lot of motion in the frame, so motion detection is out.

The trigger may not be physical - it could be generated form a smart phone for example - imagine it is a sport being played and we wish to record a significant event such as a home run, or touchdown, and the event is triggered by an onlooker - by the time they signal the event, it has already passed, which is why we need to timeslip back up to 30 seconds to capture the build up to the event, the eevent itself and its immediate aftermathy.

Accepted Solution

Kenneth Brown earned 1000 total points
ID: 35244874
It seems to me that the problem is finding some software that can buffer 30s video but in some temp storage, and then on demand (and also say 30s later after capturing another 30s,) commit that 60s temp storage to a single file that is somehow tagged with the time/date say, & then saved as a 'proper' file.

How about finding an app that can save video to named files in (say) 1s chunks. Keep track of these chunks in a circular buffer style, and when your event is triggered ( or rather 30s later) : flag for the set of 60 x 1s-chunk-files to be copied out to some say folder whos name represents the trigger time.

...Then offline concatenate the 60 sep files into one...

I can only think of MaxMSP/Jitter that could actually do this in my limited experience.

LVL 15

Author Closing Comment

ID: 35308632
We are going to use ffmpeg for the splicing and slicing, after capturing in one minute chunks.

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