You can perform simple video and audio editing in Pages on Mac like—trimming, looping, adjusting volume, and choosing a thumbnail for videos.
Go to the Pages app on your Mac.
Open a document with video or audio, then click the video or audio to select it.
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: Audio recorded in Pages can’t loop back and forth.
Go to the Pages app on your Mac.
Open a document with video or audio, then click the video or audio to select it.
In the Format sidebar, click the Movie or Audio tab.
Click 
next to Edit Movie or Edit Audio to show the edit tools (if necessary).
Drag the Trim sliders.
Note: You can’t trim audio that you recorded in Pages on your iPhone or iPad.
You can change the video thumbnail—the frame that’s displayed on a page to represent a video.
Go to the Pages app on your Mac.
Open a document with video, then click the video to select it.
In the Format sidebar, click the Movie tab.
Click next to Edit Movie, then drag the Poster Frame slider.
Go to the Pages app on your Mac.
Open a document with video or audio, then click the video or audio to select it.
In the Format sidebar, click the Movie or Audio tab.
Drag the volume slider.
You can set Pages to optimize the format and quality of movies and images that you add to documents.