Ah sorry, I assumed you inserted the video yourself.
If you want to extract the video as a separate file, you can
- make a copy of the PPT file
- change the extension of the copy from .pptx to .zip
- double click the zip file
- open folder 'ppt' >> open folder 'media'
- the video should be in that folder >> you can see what file type it is, maybe try to re-insert it on the slide etc.