Open your terminal and change the directory to your video directory. This process differs depending on your OS.
If you use a Linux or Unix computer and wanted to create a thumbnail of your home movie, or downloaded video clip, you can use the FFmpeg tool. FFmpeg is typically used as a video converter but it can also be used to extract images from videos. Using the image extraction process, you can set a time segment and then extract a single frame to an exported file.
Type "ffmpeg -i video.xyz -ss 00:00:05 -an -r 1 -vframes 1 -y %d.jpg" (without quotes).
Replace "video.xyz" with the video file name. Replace "00:00:05" with the time of the thumbnail you want to make in hours, minutes and seconds.