We just recently encountered a similar conundrum to this in our org,
though in our case, the issue is our inability to view embedded
videos/gifs within the PPT when viewing in the Proofing Viewer. Our
interim solution was to upload the video separately, so comments could
be made frame-by-frame there, and any feedback that was more focused on
the PPT slide content would go in the PPT proof pages. While your
situation is different, it got me thinking that one possible solution
for you could be to ...