Blog
Custom fonts for streaming subtitles
Posted by Matt Juggins on , last updated
Subtitles provide an on-screen text representation of our content and are used not only by viewers with hearing loss but by many other sections of our audience. Ensuring the readability of our subtitles on both broadcast and internet delivered services across the the different languages used within the UK is therefore of critical importance and the choice of font used has a significant impact on accessibility and legibility. BBC Research & Development has recently contributed support for the DVB Font Downloading mechanism to the dash.js project to enable the BBC to use our preferred BBC Reith sans font.
On broadcast platforms, content providers have full control over the appearance of subtitles as they are broadcast in bitmap form. Subtitles for our internet streams work differently, with the client device rendering the subtitle text. Typically, content providers don’t control the platforms to which they deliver media, and so they have limited influence over the default font used to display subtitles. There is, however, a mechanism standardised by DVB that allows the content provider to request that a downloadable font be used with the subtitles in a DASH stream (or even to indicate that the font must be used).
