Responsive Design for Personalised Subtitles
Chris J. Hughes, Mike Armstrong, Rhianne Jones, Michael Crabb · 2015 · Proceedings of the 12th International Web for All Conference (W4A) · doi:10.1145/2745555.2746650
Summary
This paper from BBC R&D and the University of Dundee proposes applying responsive web design principles to subtitle display, moving away from the legacy Teletext format that has constrained subtitling since 1979. Traditional subtitles are pre-blocked into fixed 38-character-wide lines with set timings — a format designed for early television that becomes problematic when users want to change font size or view on different devices. The responsive approach instead sends subtitles with per-word timing data and formats the subtitle blocks on the client device, adapting to screen size, user font preferences, and display capabilities. The system "atomizes" subtitles into individual timed words, then dynamically re-blocks them using rules that consider character widths, semantic breaks (punctuation, speaker changes), and display area constraints. The prototype is built as an enhanced HTML5 video player using JavaScript and CSS, with subtitle positioning controlled by polygon-defined display regions. The system supports personalisation of font type (including dyslexia-friendly fonts), font size, text background (opaque, semi-transparent, or outlined), speaker identification colours (remappable for colour vision deficiencies), and subtitle positioning (overlaid on video or placed above/below).
Key findings
A study with 26 participants showed substantial variation in preferred subtitle font sizes, ranging from 14px to 30px across two BBC video clips, demonstrating that one-size-fits-all subtitling is inadequate. Participants valued both the ability to resize text and the system's intelligent re-blocking that adjusted the amount of text displayed per block when font size changed — preventing subtitles from obscuring too much video when larger fonts were chosen. One participant noted that larger subtitles made them feel like they could "hear it better," while another preferred seeing more text at once because "it makes more sense rather than splitting up into shorter sentences." The paper also presents creative possibilities enabled by the responsive approach, including speech-bubble-style subtitles positioned near speakers, word-by-word fade-in animations synced to audio, and the ability to cascade user preferences across multiple devices. The system can import existing STL and TTML subtitle files and atomize them into per-word timings either through phonetic alignment or simple interpolation.
Relevance
This research addresses a fundamental limitation in subtitle delivery that persists today: the mismatch between fixed-format subtitling inherited from broadcast television and the diverse device ecosystem of modern web video consumption. The responsive subtitling approach is directly relevant to WCAG 1.4.4 (Resize text) and the broader principle that users should be able to adapt content presentation to their needs. For accessibility practitioners, the key insight is that personalisation of subtitles goes beyond simply offering font size options — it requires rethinking the subtitle data model to enable intelligent re-formatting. The work also highlights the intersection of subtitle accessibility with cognitive disabilities (dyslexia-friendly fonts), visual impairments (resizable text), colour vision deficiencies (remappable speaker colours), and autism (benefiting from additional contextual information). As web-based video continues to dominate content consumption, the principles outlined here remain highly relevant to building truly accessible media experiences.
Tags: subtitles · captions · responsive design · video accessibility · personalization · deaf and hard of hearing · web video · media accessibility
Standards referenced: WCAG 2.0