What's inside an EPUB?

- [Narrator] Let's take a peek inside the actual ePubs components, because I think it helps anyone who is working with ebooks to understand what makes up an epub. I have open, behind my finder window, the English Cottage Gardens refillable ePub. Let's look at it, if you haven't used ADE, Adobe digital editions, up till now it's a pretty good ebook reader available for both Mac and Windows. I'm looking at it right now in double page view. It defaults to single page view so if yours looks like that just go up to the reading menu and chose double page view.

Here's the navigational TOC and I can jump back and forth. It's just a regular epub, but let's take a look at the inside of this epub. I am going to go back to the finder, now if I were on windows I could just rename this file to .zip instead of .epub I could just actually edit the file name and when I do that I would get a warning in both windows and Mac. In windows it'll work, in Macintosh it doesn't. That is I can change this to .zip in windows and then chose extract all from the right click menu.

Like you would with any zip file. Then I would end up with the component files, but on the Macintosh for what ever reason that doesn't work right. Instead I use this utility called eCanCrusher that is available for both Mac and Windows. You can download it from their website, it's a fee utility, just go right here to eCanCrusher from macrowin and all the links are in my epub resources PDF that you can download. Okay, so we have this file and I'm just going to drag and drop it right on to eCanCrusher though I could always just double click the app and then add it that way.

I'm just a big fan of drag and dropping, so I'm going to bring it right here. It immediately cracks it open into it's component files inside this folder. Let's take a look at some of these files. You make this larger, now inside the OEBPS folder this is where you are going to find all the content for your ebook. The metainf and the minetype these are just control files so you don't need to worry about that. What's interesting is that you can see that everyone of these pages is an html page.

In fact I could open this up in a browser, so if I right clicked here and chose open with let's go back to Chrome there it is in Chrome. Isn't that cool? So it is just an actual web page. It's referring to the CSS, or cascading style sheets, that were generated by which ever program created this epub. Any fonts that were embedded are also here, though they have been down sampled to just use the characters just used in the ebook. That is why they're smaller than normal.

The images are here as well, here is the cover image. Here are some of the images you see in the book itself. Then there is a separate html file just for the cover, and then there is a very important file called Content.opf and depending on the epub that you crack open it might have a different name, but it will always end with that opf. To see the insides of this content.opf you could open it up with any text editor. I'm going to open it with BB edit on the Mac. You can download BB edit from BareBones software, it is only available for the Mac and it's free.

On windows you would use a program called notepad plus. Again that link will be in the PDF. So here I'm just going to drag and drop this file onto BB edit, so it opens up and you can see that it is written it looks like a html file but it actually contains a really important management information. It is kind of like the bill of lading for this epub. It's the brains for the epub software, it is what the epub software looks for it lists all of the metadata on the top.

Like the tile and when it was published. It lists every single file that is included in this epub. So all those html files you'll see here as well as links to the CSS file, and the fonts, and the images, and so on. Then at the very bottom it has the spine section and this is what tells the epub reader after this document is opened then if the person swipes right open up this next html file, and this next html file. So it shows the order of the html files that should appear while the person is navigating the epub.

Then to quickly jump to the cover or the Table of Contents or the text that appears here. Any program that you use to export to epub will create this for you, or if you're a genius you could actually write it by hand. You can see it is just a simple text file. There's one other thing that I want to show you. That is every epub has to have a Table of Contents document that will appear when somebody taps, or clicks on, the navigational Table of Contents icon. Here we have two of them, one for epub 3 and one for epub 2 readers, and I'll talk about the difference between those in another video.

This document is simply, let's open up this one in BB edit as well. It shows the names of the entries in the TOC and which html file should open when somebody clicks on there. That's all, pretty simple document. It's not very long as you can see. Now that we know the contents of an epub you can understand why if you need to edit an epub you should know a little about html and css. But the best thing about epub is that after it's been zipped up or recompressed into the .epub extension then this epub can be read on any device or ereader without being connected to the internet.

So it's like a self enclosed tiny little website that you can access anywhere. That's what's cool about epubs.