You appear to have two invalid files. the video and the .jpg.
Look in iBooksAuthor Help files, graphics and media or open your iTunesConnect >Deliver your Content, there on the top right of page you see a number of PDFs to download...including the Asset guide.
I suggest to delete the video and .jpg from your book. The image can be Maximum of size 2048 x 1536 change for portrait, or 1024 x 748 or sizes below either to suit your layout.
Your video file is the wrong format and needs converting. The asset guide and the help files will show you what is acceptable. If you have no converters, Google - Miro ... downloads on a 14 day trial!
There is little point in opening / unzipping your .iba file if you do not feel comfortable, but you do not need an " unzipper". If you want to investigate book the file contents, first duplicate your book save it as Test or whatever.
Change the suffix from .iba to .zip and confirm.
Your priority is to check out the two invalid files..and make changes.