It is suggested to take the snapshot during the preview in the media library. Below are the steps to figure it out:
1. Import the original file to the media library.
2. Double click the video in the media library to playback it in full quality in the preview window.
3. During the preview, you can take the snapshot as you want, see the picture below:
4. After that, the snapshot will be shown automatically in the media library. right-click on the snapshot then hit Reveal in Explorer to find the path where it is saved automatically on your pc, see the picture below: