In your assets library, select the video file with which you want to work.
On the ribbon, click the Manage tab.
In the Actions group, click the Edit Properties button.
In the the Edit Properties dialog box, click the Change Thumbnail link.
From the three options that appear, click the Capture Thumbnail From Video option.
In the video window that opens, click the Play button.
Click the Camera icon to capture the image.
On the Video Properties page, click Save.
