EPUB Files Deconstructed

Have you ever seen a .EPUB file? It contains all the information required for an electronic document. It stands for electronic publication. I was looking into EPUB files because I am working on a personal project that involves reading and language learning. I wanted to create a basic e-reader that functions with the EPUB standard.

The EPUB Standard

The EPUB Format became the standard for creating and distributing digital documents, especially books. The standard is currently maintained by the w3c (world wide web consortium) community. There have been several iterations of the standard in order to improve the older version. The current versioning is at 3.3 as of 2023.

If you look at an EPUB file with a text reader you get this:

This crazy encoding is a good indication that the file is a compressed version of what you want. When you unzip the EPUB file, you get the following files and folders:

What makes EPUB particularly powerful is its foundation in web technologies. At its core, an EPUB file is essentially a specialized ZIP archive containing HTML, CSS, and other web-standard files, arranged in a specific structure. This means publishers can leverage familiar web development tools while ensuring their content remains highly portable and adaptable to different screen sizes and reading devices. The HTML files reside in the OEBPS folder.

EPUB's key strengths lie in its robustness. HTML is so ubiquitous because of the web, and so it makes a lot of sense for that language to also provide reliable support for displaying reading content. HTML allows readers to customize font sizes, line spacing, and even switch between themes without compromising the document's structure. In the latest versions of EPUB, there is support for audio, video, and javascript support. Publishers can now create multimedia experiences while maintaining backward compatibility with older reading systems.

Structure of an EPUB File

  • The META-INF directory contains the container.xml file, which points to the package document (typically content.opf)
  • The OEBPS (Open eBook Publication Structure) folder houses the actual content:
    • XHTML files containing the book's text
    • CSS files for styling
    • Images and other media
    • The content.opf file, which serves as a manifest of all included files
    • The toc.ncx (or nav.xhtml in EPUB3) file that defines the table of contents

Creating an E-Reader Application 

For developers interested in building their own e-reader application, understanding these components is crucial. The process involves:

  1. Unzipping the EPUB file
  2. Parsing the container.xml to locate the content.opf
  3. Reading the content.opf to understand the document structure and included files
  4. Rendering the XHTML content according to the CSS styling
  5. Implementing navigation using the table of contents

Thanks to this standardized structure, developers can focus on creating unique reading experiences while relying on well-established web technologies. Whether you're building a simple text viewer or a full-featured reading application with annotation support, the EPUB standard provides a solid foundation to build upon.

There are a lot of tools and libraries that have been developed to help people read an EPUB file and parse it. In my personal project, I have been working in flutter. In flutter, there are several packages such as epub_view that have been helpful for displaying content how it fits in my application and not in an HTML environment.

For language learners and educators, EPUB's are interesting because it brings the world's digital information and literature to the masses. I am interested in how literature can assist the language learning population to help people learn foreign languages. If you are interested in this task too, reach out and we can build together. 

Getting Started 

Language learning is one specific use case, but if you're interested in working with EPUB files in general, several open-source libraries can help you parse and manipulate these files programmatically. Popular choices include EPUB.js for JavaScript developers and libraries like ebooklib for Python-based projects. These tools abstract away much of the complexity in handling EPUB files, letting you focus on building innovative reading experiences, and not getting too bogged down in the parsing of the actually EPUB files.

Whether you're a developer, publisher, or simply curious about digital publishing standards, understanding EPUB's overall structure and capabilities is a significant step to building cool reading tools.

Comments

Post a Comment

Popular posts from this blog

Phonetic Posteriorgrams

Image
For my MSc dissertation, I am trying to synthesize speech with variable L2 accent strength. There are a few ways to approach this. The "fastest" and "easiest" way is to have the perfect dataset that has reliable labels for accent strength on each utterance. There are two problems with this approach. First, this dataset would be incredibly difficult and expensive to create. Second, it is difficult to get a trusted label for "accent strength" that is also consistent across the dataset. What does accent strength even mean and how would it be measured non-subjectively? I was talking about this problem with one of the PhD candidates in the CSTR group, and she told me to look into phonetic posteriorgrams. Since then, I have tried to read a bit about them. I wanted to explain them in this post.  What is a Phonetic Posteriorgram? A phonetic posteriorgram (PPG) is well described in it's name. Phonetic indicates that we are talking about phonemes, or speech cate...
Read more

The Hard Part About Speech

Image
The rise of Large Language Models (LLM) in recent years has certainly made a lot of people see the world differently. I believe that many people are more interested in statistics, machine learning, computer science, and linguistics because of these fantastic advancements, myself included. As I have studied intensely at the University of Edinburgh over the last year, I have realized more about what these kinds of models do, and how they relate to the bigger picture of modeling functions in general. All of these models are doing some form of function approximation/prediction task. Language models like GPT or BERT are simply predicting the next word token given the context, Automatic Speech Recognizers (ASR) like Whisper are predicting the text output given a waveform, Text to Speech (TTS) models like Amazon Polly are trying to predict the spectrogram or waveform given the textual input and who it should sound like. There is always a task, a dependency, data, and a metric to measure that ...
Read more

Language Identification Project

Image
I wanted to complete some practice problems and build a small basic portfolio of small tech projects that showcase some of my recent learning at the University of Edinburgh. I have taken several courses about natural language processing (NLP) at uni.  NLP is a very wide term for a variety of different tasks, for example, text classification, named entity recognition, machine translation, language modeling, etc. This project was just a simple text classification task. I wanted to input text and have a model predict which language it is. Find the code on my  Github , and my steps that I took to create the project below. Hope this helps facilitate your learning too. Step 1: Find data Foundational to any project involving any sort of prediction. You need data and preferably a lot of it. I wanted to predict language, and one corpus of language data that I already knew about from school was the Europarl Dataset . This is a corpus of EU meetings that are translated into the languages...
Read more