Navigable audio-only EPUB3 Guidelines

Guidelines for Navigable Audio Only EPUB 3 Publications

Version: 1.0
Release date: April 24, 2015

edited by Avneesh Singh, integrating comments from George Kerscher, Romain Deltour & members of TIES production subgroup

Overview

The document provides guidelines for Navigable audio only EPUB 3 publications. The objective of the document is to provide guidance to audio books production centres, production tools developers & reading system developers for production and rendering of the EPUB 3 publications that mainly consists of audio and possesses the capability to navigate to sections, pages & other skippable structures.

Background

The guidelines are based on EPUB 3.01 specifications, available at
http://www.idpf.org/epub/301/spec/epub-overview.html
And
http://www.idpf.org/epub/301/spec/epub-mediaoverlays.html

Envisioned Use

  1. Within the DAISY Consortium hundreds of thousands of titles have been produced that are audio only with navigation that conform to the DAISY 2.02 or the DAISY 3 specifications. It is expected that over time these will be converted to this specification.
  2. The commercial audio book industry may find that this set of guidelines useful in the future developments of audio books that conform to these guidelines and EPUB 3.0.1. A single file for distribution and the broad range of support in EPUB reading systems may make these guidelines very attractive.

Flow of control with respect to the DAISY specifications

Functionally, the EPUB 3.0.1 Media Overlays specifications are somewhat similar to the DAISY specifications. In both the specifications, the synchronization between text and audio is achieved through a smil file, which is called Media Overlays document in EPUB 3.
But there is a little difference in them also. The flow of control in EPUB 3 Media Overlays is a little different from that in DAISY specifications. Unlike DAISY specifications, the Navigation Document does not refer to the smil files directly in EPUB 3. Instead, the Navigation Document refers to the Content Document, and the Content Document is associated to the corresponding smil file. Therefore, the control of synchronized media in EPUB 3 will go through the Content Document.

Guidelines

1. Structure of the file set

  1. The Navigable audio only publication MUST contain separate Navigation Document & Content Documents to prevent circular references.
  2. Multiple Content Documents are RECOMMENDED to ensure multiple smil files of smaller size. Small size of smil file is essential for reading systems with low processing power.
  3. Recommended granularity of Content Document & corresponding smil files is: one Content Document for each heading.

2. Navigation & Skippable Structures

2.1. Pages
  1. If the publication has pages, the Navigation Document MUST have one page-list, and the list items in the page-list MUST reference the page break mark-up in the Content Documents. EPUB:type=”page-list” MUST be used for nav element containing the page list.
2.2. Skippable notes
  1. If the publication has skippable structures like footnotes, then the Navigation Document MAY have nav elements containing a list of references to the skippable structures in the Content Documents. EPUB:type=”footnotes” MUST be used for the nav element containing the references to the footnotes while EPUB:type=”landmarks” MAY be used for rearnotes, notes, help etc. There MUST be at most one nav element for footnotes and at most 1 for landmarks.
    Important note: The value of EPUB:type attribute is yet not explicitly defined for collection of skippable structures like rearnotes, notes etc. It will be supported by the EDUPUB profile in the future. Please keep track of EDUPUB profile at http://www.idpf.org/epub/profiles/edu/EDUPUBContentModel/ContentModel.html
  2. Skippable structures in the Content Document MUST be represented by skippable elements, which SHOULD contain text for representing the skippable structure, for example <aside id="s1" epub:type="sidebar"><p>sidebar-1</p></aside>
  3. The smil elements representing the skippable structures MUST reference to the skippable element in the Content Document, while the smil elements following the skippable structure SHOULD refer to a place folder situated below the skippable element in the Content Document. The place folder MAY be a text placed in html 5 element like div or p.
    for example <p id=”text1”>Main content continues</p>

3. Media Overlays references to Content Document

Media Overlays are designed for text audio synchronization, but in audio only EPUB 3 publications, text events are less as compared to audio, & the Content Document will mainly contain the text for headings & pages. The RECOMMENDED approaches for synchronizing partial text with audio are as follows:

  1. Smil events that have no text association SHOULD refer to the Content Document elements corresponding to the text content like heading or page that precedes the smil event. This approach is more suitable for leisure reading books where the audio events are in large numbers & high precision is not expected.
  2. Smil events that have no text association SHOULD refer to dummy text in the Content Document, such that each smil event refers to a unique text fragment. This approach is more suitable for text books because functionalities like the bookmarks will work precisely with this approach.

4. Metadata

  1. EPUB 3.0.1 specifications yet do not have metadata specific to audio only publications. Till the appropriate metadata is included in the EPUB 3.x specifications, the Media Overlays metadata MUST be used.
    Important note: The guidelines working group recognizes that metadata for identifying the Navigable audio only publication is important for the distribution systems. It will be incorporated in the specifications in the future.

5. Visual rendering

  1. The visual rendering of the Content Documents is mostly controlled by the reading systems.
    However, it is OPTIONAL to hide the Content Document on the production side, if the production centre wants to purposefully impose a visual rendering behaviour on the reading systems.

Conformance Statements

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", “MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119.
https://www.ietf.org/rfc/rfc2119.txt

Samples

File name/ download url Size Description
The Story of the Three Little Pigs-dummy text.epub 4.2 MB Sample publication with dummy text in the Content Document
The Story of the Three Little Pigs.epub 4.2 MB Sample publication without dummy text
Climbing The Highest Mountain.epub 2 MB Sample publication with skippable structures

Guidelines last edited: July 22, 2014