IMSC Support in Accurate Player

Accurate Video
Nov 30, 2020

With the 4.0 release of Accurate Player, we’re pleased to announce support for the Internet Media Subtitles and Captions (IMSC) subtitle standard!

IMSC, recently ratified by the W3C, is used around the world by OTT services, such as Netflix and broadcasters like the BBC. Many platforms and players also support it, including Apple iOS devices. IMSC supports a wide range of world languages and scripts and rich styling. In addition to text-based subtitles, IMSC also supports PNG subtitles.

For technical operators, it is essential to verify and QC subtitle absolute positioning and on-screen formatting. Whether for cinematic release, distribution to VOD/OTT platforms, or available through inflight entertainment systems, subtitles that are poorly positioned, or are otherwise unintelligible, ruin the viewing experience. And while desktop subtitling applications can fix issues easily, modern, globally distributed QC and localization teams need to be able to consistently verify subtitle content, for any viewing platform, managed directly in cloud storage, to avoid downloading or egress fees.

This is where desktop applications and legacy on-premise workflows become slow, clunky, and are poorly integrated (if at all), to support modern remote working.

Although easy to use, Web Video Text Tracks (WebVTT) SRT can be perceived as a blunt tool.

Enter TTML and IMSC

Timed Text Markup Language (TTML) is not a new standard, defined as “...a content type that represents timed text media for the purpose of interchange among authoring systems. Timed text is textual information that is intrinsically or extrinsically associated with timing information.” ( it has become a standard for exchanging subtitle and caption metadata. However, to display this information as an internet end-point something else is needed. The IMSC standard, also defined by W3, is the gateway needed.

This subtitle standard, defined as “...a file format for representing subtitles and captions. It uses XML to describe content, timing, layout, and styling. IMSC is very similar to HTML and CSS in concept — in fact, most IMSC styles have a direct equivalent in CSS.

In version 4.0.0 of the Accurate player, we’ve introduced the ability to view IMSC based subtitles. So what does IMSC support in Accurate Player really mean? In this first iteration, we support the playback of IMSC files that are stored separately from the video file/stream itself. This is useful as it means that it works exactly the same regardless of whether you’re streaming media progressively, or using Adaptive Bitrate (ABR) technology, as your preferred method of streaming content



In the Accurate Player user interface, you have complete visibility of the styling and positioning of subtitle cues. Accessibility is great, but if you’re going to validate your media, it must be presented in the same way as your end users will experience it! Our implementation doesn’t rely on your web browser's built-in rendering, which can cause issues, such as not being able to remove the background color of subtitles in certain web browsers for accessibility reasons.

Future updates will include IMSC support in Accurate Video, which in turn will allow for subtitle modification and exporting of IMSC/TTML metadata. But in the meantime, if you want to take your pipe and smoke, you’re welcome.

To get more information around Any questions regarding this new feature or anything else regarding our products can be sent to