Enabling Professional-Quality Online Video: New Specifications for Interoperable Captioning

April 25th, 2013

Video captioning on the Web is about to get significantly better, putting in place another critical building block for enabling professional-quality online video delivery and playback. To achieve the experience of broadcast television, the Web needs to provide captioning capabilities including word highlighting, tight synchronization between captions and spoken word, flexible caption positioning, caption styling, and caption animations – all of which are part of a recently published profile specification from the W3C Timed Text Working Group (TTWG). Microsoft has joined with content owners, video distributors, and device providers in developing the specifications to ensure interoperability and streamline closed caption authoring and delivery. For content and tool providers, the specification enables authoring of interoperable caption files for delivery to a wide variety of software and devices, while meeting evolving industry requirements.

Captioning is an intrinsic part of any professional-quality video experience—and the impact goes far beyond enabling the hearing impaired to gain full access to the video content. Captions are turned on in loud environments, such as at the gym. Captioning is used to help us all understand foreign language films. Of course, I’m surely not the only person who turns on captions to better understand difficult accents in movies streamed on Netflix.

In February 2013, Microsoft joined industry stakeholders in the W3C Timed Text Working Group (TTWG) to deliver the TTML Simple Delivery Profile for Closed Captions (SDP-US) profile specification. This new profile was created with input from media industry experts from DECE, SMPTE, EBU and industry players including Adobe, MovieLabs, NBC Universal, Cox, Apple, Netflix and Microsoft.

SDP-US is based on Timed Text Markup Language (TTML) (a caption interchange specification that has been used in the professional video industry for years) and clearly defines key caption format features like layout, style, timing and content requirements, enabling content authors and tool providers to easily create interoperable caption files that meet evolving industry requirements. SDP-US will help streamline creation of closed captions to deliver media content to the Web across a wide variety of software and devices – in a browser like Internet Explorer, on devices such as Xbox or through applications built using the Microsoft Media Player Framework

Internet Explorer was one of the first browsers to include early support for HTML5-based video captioning via the <track> element with TTML and WebVTT file formats.  Since then, we’ve heard clear feedback from content authors: They need an interoperable, simple and full-featured captioning solution that meets emerging requirements for browsers and other software on Internet-connected devices.  SDP-US will meet this need by defining a streamlined set of captioning capabilities for the HTML5 <track> element.  Developers will be able to add captioning to an HTML5 video by providing a caption file that contains a styled text representation of the video dialog or actions and by using the <track> element to render and display the contents of that file. 

To illustrate some of the power of the new SDP-US captioning specification, here’s an example of how Internet Explorer renders captions with a default plain text style and position:

Captioning in IE10 always looked like this

With SDP-US, caption authors have much more flexibility in caption positioning and styling, as shown in the below examples:

SDP-US allows captions to be placed anywhere on the screen

It allows caption text to be emphasized and colored

And caption regions can be filled with color

Professional-quality online video is a forthcoming reality, enabled by emerging Web specifications and powerful content delivery infrastructure. Captioning is an important building block for enabling professional-quality video, and Microsoft is actively working with industry partners to enable rich captioning experiences. If you are working on Internet video, we invite you to review the new SDP-US profile, join the industry discussion, start considering how your caption content can adapt to SDP-US, and let us have your feedback.

— Sandeep Singhal, Group Program Manager, Internet Explorer