Trigger recording of minimum delay based on activity in video

[mgraupe]

Deall all,

I would very much appreciate help with the implementation described below. Thanks in advance.

I would like to trigger the recording (activate videoWriter) whenever there is movement in a certain area of a video.

• The recording should be active at least for a certain duration (let's say 30 sec).
• The recording should continue, remain active, as long as there is ongoing activity in the video.
• Furthermore, the active recording should be signaled to the pin of the Arduino, i.e., the pin should be high as long as the recording is active.

I managed to trigger videos based on the activity. But all videos are of the duration set in the delay node. How can it remain active due to further activity threshold crossings? And how to signal it to an Arduino?

Thanks,
Michael

[Mateo-Lopez-Espejo]

Hey Michael.

I was trying to set some LED to stay on for n seconds as long as an animal was doing something. not too different from your task at heart.

The solution I came up with was to use CreateObservable which simply generates a sequence of False then True after a given delay (in your case 30 s).

Every time the animal fulfills the condition, a new observable sequence is generated. Then the Switch node downstream selects the last observable sequence, effectively restarting the countdown.

The rest is straightforward: if the countdown lapses, the switch emits at True which passes the condition and triggers the take until.

This is hell of a hack, but it has been working so far for me. Hopefully it works for you and someone can come up with a more elegant/straightforward approach.

Cheers,
Mateo

[mgraupe]

Dear Mateo,

Amazing! Your implementation works like a charm! And I find it quite minimalistic. Thanks a lot for the suggestion.

I have extended the workflow such that an digital pin on the Arduino (connected to an LED) switches one 2 sec after the video recording start and switches off two seconds before the recording end. (I need this for synching images to other modalities.)

There is one aspect which I haven't managed to implement yet. Maybe you have idea?
I would like to introduce a delay in the video stream connected to VideoWriter. That way, I want to assure that the video is recorded already before (by a defined interval) the event which leads to the trigger. There is a delay node in that video stream btw. image and VideoWriter in my workflow (see image). However, this delay seems to delay the saving of the file but not the video stream.
Any ideas how to introduce the delay correctly to capture what happened before and during the trigger event?

Thank you so much!

Cheers,
Michael