You can use REST hook from WCS to backend
/StreamStatusEvent which contains fields:
"name" - by which you can identify the stream
"status" - from which the backend learns the current status of the stream.
For VOD stream:
status: PUBLISHING means the beginning of the publication, i.e. the beginning of the video
status: DISCONNECTED means stop publishing, i.e. the end of the video
also,
status: DISCONNECTED can mean stopping publication by time, if the VOD stream has no subscribers within 60 seconds (default)
More
https://docs.flashphoner.com/display/WCS52EN/Type+3+-+the+event