I am making an application that saves and plays video files.

The flow is
1. Run the camera using RawImage → WebCamTexture
2. Record and save the resources taken by the camera using OpenCVForUnity.VideoWriter.
4. Tap the thumbnail image to play it with OpenCVForUnity.VideoCapture.

You can do 1, 2 and 4 without any problem, but how to create a thumbnail image of 3 is
I don't know yet.

Just save the first (first) Mat and save it separately when saving with VideoWriter
Is there a way?

Or are there any good assets, methods or methods?

PC: Windows 10
Unity 2019.4.0f1
Language: C #