by Andrew Kirkpatrick

 Comments (8)


October 3, 2011

This post is subject to Adobe's Terms of Use.

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.


  • By Deaf - 1:35 PM on November 11, 2011  

    Speaking of captioning, none of videos on Adobe TV website are captioned. I’m one of 37 millions of deaf and hard of hearing people in the states. Why? This is very ironic when a giant like you is trumpeting about accessibility. I left a message in feedback a few weeks ago and did not hear back from you. The video pages have a button to request a transcript. Captions are not to be requested – they are required to provide a full access to those who do not ave access to audio. Thanks.

    • By akirkpat - 11:01 AM on November 16, 2011  

      I’ll grant you that not enough videos on Adobe TV are captioned, but many are. For example, if you look at Julieanne Kost’s video listing you’ll find that about a third are captioned. If you look at the CS5.5 Web Premium video list you’ll see that about 75% are captioned. I’m working to get a commitment for all to be captioned, but we’re not there yet.

  • By Golam Maruf - 7:35 PM on May 9, 2012  

    Great thing. Will it work with multi-bit rate HTTP Dynamic Steaming with f4m manifest?
    The new OSMF player is out. Can we integrate this plugin with the new OSMF player for HDS – f4m Manifest files? Please let me know.

    • By AWK - 1:45 PM on May 10, 2012  

      Maruf, this work is still in early stages, so this is a bit of an early preview of a possible solution but a final solution may take a different form. It does work with HTTP Dynamic Streaming with f4m, there is an example in the source drectory.

  • By Mateo - 7:50 PM on June 27, 2012  

    I understand that the SMPTE-TT can come in different flavors. Can you provide a sample SMPTE-TT file that is supported by your plugin?

  • By Kevin Campbell - 1:05 PM on July 2, 2012  

    Our client has a large library of DFXP/TTML captioning files, and they now need to support SMPTE-TT. Their current OSMF video player is using an earlier captioning plugin. Is the new SMPTE-TT plugin backwards compatible with DFXP formatted files?

    I’ve tested TTML files using your SMTPETTPluginTest project in sourceforge, and AS errors related to styling were present when testing a DFXP file. Can you recommend a best practice for dealing with multiple formats using OSMF pluigns? Thanks.

  • By Sz - 7:55 PM on November 20, 2012  

    Nice articel.
    So, OSMF supports TTML and SMPTE-TT(future) and that’s client side right? I think Adobe Media server currently only support CEA-608/708 embedded in video. Does that mean that the server will support TTML and SMPTE-TT in the future with HDS? Where can I find more information on Adobe Media server plans about Closed caption like this?