There are a few ways to shorten a video for Instagram, but the most common is to use a quick and easy tool called " trim ." To use trim , you first need to create a new video. Then, open up the " trim " tool and select the length of your video you want to shorten. Next, click on the " start trimming" button and wait for the tool to start working. Once it’s started, just keep moving the mouse around until your video is shortened to its original length.