Editing movie

You're absolutely right on this. PowerPoint's video editing abilities are pretty basic right now. You can't clip a segment from the middle of a recorded video without using a third-party video editing program, but here's something that might let you achieve more-or-less the same effect in PowerPoint:

1. Set a bookmark on the exact spot where you want to "cut" the video.
2. Set another bookmark on the exact spot where you want to "resume" the video."
3. Add a seek animation to the video (seek will appear disabled until you have at least one bookmark), set it to seek to Bookmark 2, and set it to trigger on Bookmark 1.

On playback, the seek will be instantaneous, so the effect will be a jump across the middle of the video. However, please be aware that bookmarks cannot be moved, only deleted, and that will wreck your triggers. Also, the file still technically contains the cut segment, so it won't be any smaller. And other timings, such as a slide transitions, won't reflect the shorter duration of the video, which may make other animation sequences harder to plan.

In short, it's often easier just to edit the video outside of PowerPoint or reshoot to remove the goof.

Microsoft could do a lot to make this easier to use with better UI in PowerPoint, or a dedicated video editor. PowerPoint is a great tool for animation, but is woefully lacking for producing polished video.