by Andrew Kirkpatrick, Group Product Manager, Accessibility
Supporting accessibility is an important aspect of supporting video, and closed captioning is of particular interest lately with the release of the FCC’s proposed rules for captioning. The FCC’s proposed rules are to fulfill the requirements of the 21st Century Communications and Video Accessibility Act of 2010 and are specifically targeted to broadcast video when delivered via the Internet.
A key question around captioning is the best file format for caption data. The W3C’s TTML is a standards which is commonly used, and SMPTE has extended this standard for an additional format, commonly known as SMPTE-TT. In addition to these, the WHAT-WG recently invented a new format, named WebVTT (based on a previous format, SRT). Authors are not surprisingly unsure as to the right format to use. As appealing as a single caption format may be, it currently seems unlikely that a single format will meet the needs of all providers of captions.
Adobe has helped those delivering video via Flash deliver closed captioning for several years. Flash CS3 included support for TTML (then known as DFXP) back in 2007 and has provided similar support for TTML in the Open Source Media Framework (OSMF). Our most current work on captioning addresses other standards for captioning:
- Support for SMPTE-TT in OSMF. We’ve developed a plugin for OSMF to support SMPTE-TT. This is freely available and licensed under the BSD software license, so even if you aren’t using OSMF it is possible to utilize the source code to support SMPTE-TT in other environments. This plugin supports robust positioning and formatting for closed captions.
- Participation in a community group for WebVTT at the W3C. WebVTT is still new and needs work to fully support the necessary functionality for captions. The advantage of this work happening at the W3C is that there is a greater opportunity for additional input. As this is a format that browser vendors have expressed interest in implementing, it is important for developers and end users to join the community group and weigh in on strengths and weaknesses of the format to help ensure that the spec provides support which is sufficient for the needs of all concerned. Adobe has joined this group to help ensure that this is true for the WebVTT community spec being drafted.
Our intent is to support what our customers want, and we have some customers who want each of these three formats. As a result we’re engaged with multiple efforts. The bottom line for Adobe is that end users who depend on captions need complete information to provide access to video and audio content and developers and video providers need efficient solutions that fit into their overall video workflow. Whether providing implementations for a developed standard or engaging in a standards development activity, we will work to ensure that both end user and video provider needs are met.