Add a poster frame to your video
When you add a poster frame, it provides viewers with a preview image of your video.
Use a frame from your video as a poster frame
Click Play to begin playing the video.
Play the video until you see the frame that you want to use as your poster frame, and then click Pause.
Under Video Tools, on the Format tab, in the Set Poster Frame group, and then click Current Frame.
Use a picture as a poster frame
Select the video on the slide.
Under Video Tools, on the Format tab, in the Adjust group, click Poster Frame, and then click Image from file.