Implementing Closed Captioning for DTV

The Federal Communications Commission (FCC) rules impose obligations on broadcasters for captioning of digital television (DTV) programs, but there has been some uncertainty over exactly what is required. This paper sets out the main requirements defined by the FCC rules, summarizes what broadcasters should be doing to meet those requirements, and provides guidance on implementing the various links in the chain from caption creation through to emission. A method for transport of DTV closed captions is described using data services in the vertical ancillary data space of serial digital video signals, and several methods for feeding caption data to the ATSC encoder are identified. RULES AND REGULATIONS FCC Rules Since July 1, 2002, US broadcasters have been required to provide closed captioning on at least some of their programs transmitted on DTV channels. The core responsibilities of broadcasters were defined in the FCC Report and Order (R&O) issued July 21, 2000, regarding DTV Closed Captions (DTVCC) [9]. The FCC R&O amended Part 15 of the FCC rules, adopting technical standards for the display of closed captions on digital television receivers. It adopted into the rules Section 9 of industry standard EIA-708 (now CEA-708-B) [6], specifying the decoding and display of closed captioning for DTV systems. For informational purposes it also incorporated by reference the remaining sections of the standard, which specify the encoding, delivery and other aspects of DTVCC. The R&O amended Part 79 of the rules to require transmitted closed captioning to reflect the changes in Part 15 and to require all caption data to be passed intact through program distribution facilities in a format consistent with Part 15, unless such programming is recaptioned or captions are reformatted. The R&O also clarified the schedule for including closed captions in digital programming. No distinction is made in the FCC rules between DTVCC for high definition or for standard definition programming; requirements are the same for both. The R&O makes clear that during the transition period to digital television, DTVCC in accordance with CEA708-B may be derived from legacy CEA-608-B [5] (analog) captions as well as from native 708 authoring. It also confirms that to count captioned DTV programming hours towards the captioning total for each channel, the broadcast DTV signal must include both CEA-708-B and CEA-608-B caption data. Receivers The rules require all DTV set-top boxes and DTV receivers with a screen height of at least 7.8 inches (the height of a 13-inch 4:3 display) manufactured after July 1, 2001 to include a caption decoder complying with Section 9 of CEA-708-B. Such devices shall provide the user with control of caption font, size, color, edges, and background. Decoders must be able to decode the six standard services in CEA-708-B and allow users to choose at least one for display. Set-top boxes that have an analog NTSC output shall insert 608 caption data carried in the DTV signal into line 21 of the NTSC video output. Cable Carriage The rules require digital television programming with CEA-708-B caption data services to be delivered to digital cable subscribers with captioning intact. Programming Requirements and Schedule The FCC rules allow for a phased introduction of captioning as follows (note that at this time the term “channel” has not been clarified in relation to multicast