EPUB Media Overlays support

[vers-one]

Description

EPUB 3.2 specification lets EPUB books to declare media overlays which are essentially just embedded audio narrations synchronized with the text content. A reading software can use this information to highlight the words in the text as a narrator speaks.

This was first implemented by Apple as a non-standard extension for EPUB 2 books (under the name of Read Aloud). Later this feature was added to the EPUB 3 standard.

There is only a small amount of EPUB 3 books that contain media overlays and very few reader apps that actually support them. But nevertheless, it might be useful to have such support in this library.

Proposed solution

1. Create schema data types that reflect all XML elements in the Media Overlays specification.
2. Parse all SMIL files found in the EPUB book into these data types.

Note that this enhancement only parses SMIL files but doesn't perform any post-processing for the parsed data. There is a subsequent enhancement #84 which will expose the parsed data as easy to consume narration objects on the EpubBook level.

Additional context

EPUB Media Overlays 3.2 specification: https://www.w3.org/publishing/epub32/epub-mediaoverlays.html