Hi. I know this thread is a few years old, but I've just discovered a trick for locating hidden asset files that are inflating the overall story file size and I'm excited to share it.
I had a single embedded video in my story, but the overall file size was more than twice the video size, although the Media Library inventory couldn't account for it. So I used a trick I learned about here on the community site (thank you contributors!) to find out what was taking up so much space: (1) make a copy of your .story file, (2) change the extension of your copy from .story to .zip, (3) extract/unzip the file, (4) find the media folder (my path was: story > media), (5) sort by size to find the largest culprit.
The thing was, even though the video was used only once on 1 slide, I found it listed twice in the media folder. Even after I deleted the single instance of it from my slides, and it disappeared from the Media Library, my overall .story file size was nearly the same (still twice the video size but there were zero videos in there now). I was stumped. So, here's the 2nd trick I used: (1) use trick 1 above but stop at step 2, (2) double-click the still zipped file to find any files in the media folder that shouldn't be there and delete them, (3) rename the file back to .story from .zip. That's it! My story was still intact and working perfectly but my file size was hugely reduced. I then added back the video that I wanted and my overall file size increased by just that video's size. My overall file size was finally what it should be (reduced by half!). So happy.
