By default, a video or audio file plays one time when you click the Play button 
. You can set it to repeat in a loop, adjust its volume, and trim it to play only part of the video or audio. For a video, you can change the poster frame that’s displayed on a sheet to represent the video.
Click to select the video or audio on the sheet.
In the Format 
sidebar, click the Movie or Audio tab.
To set media to repeat, click the Repeat pop-up menu, then choose how you want it to play:
Play in a continuous loop: Choose Loop.
Play forward and then backward: Choose Loop Back and Forth.
Note: Recorded audio can’t loop back and forth.
Click to select the video or audio on the sheet.
In the Format sidebar, click the Movie or Audio tab at the top of the sidebar.
Click the disclosure triangle next to Edit Movie or Edit Audio, then drag the Trim sliders.
Note: You can’t trim audio that you recorded in Numbers on your iOS device.
You can choose the frame that’s displayed on a sheet to represent the video.
Click to select the video on the sheet.
In the Format sidebar, click the Movie tab at the top of the sidebar.
Click the disclosure triangle next to Edit Movie, then drag the Poster Frame slider.
Click to select the video or audio or on the sheet.
In the Format sidebar, click the Movie or Audio tab at the top of the sidebar.
Drag the volume slider.
You can set Numbers to optimize the format and quality of movies and images that you add to spreadsheets.