Don't miss that in PowerPoint 2019, you can trim down video files that have been inserted into a presentation.
Simply select the video, and then click on the Playback tab under the Video Tools menu. You'll have the option to trim down the video; insert captions for it; or adjust how it appears and fades out.
Note that the video will not be saved at its new length, until the presentation is compressed. This is done under File . . . Info
It's possible to reduce the size of a presentation greatly without suffering a significant loss of quality in the video clips. After the compression is completed you will be able to save a local copy of the video at the new length.