[FFmpeg-user] How to get motion vector value for object movement detection using "mestimate" filter?

[Rajh U]

Hello,
I am using "mestimate" filter to apply motion vector to a live video stream webcam and when motion is detected would like to take snapshots.How can I do this by setting a threshold value?
I can not find any documentation of "mestimate" practical examples and how to extract it's data in real time to take snapshots.
Thanks for any advice.