Closed Captioning has become an essential part of program delivery from broadcast to streaming platforms in recent years with many insisting on its inclusion for acceptance of a program or project, and this demand will continue to increase in the coming years.
AJA offers a broad base of products that provide extensive Closed Captions (CC) support. In order to better understand which AJA products are appropriate for your Closed Captions workflow needs, we will first define the common terms used to describe the different types of Closed Captions. Following the descriptions, we will present the AJA products that are Closed Caption compatible and the standards they support.
The Closed Captioning standard for analog NTSC broadcasts in the United States. CEA- 608 captions operate on line 21 of standard definition NTSC broadcasts. CEA-608 captioning is not user adjustable. Font sizes and colors are fixed.
*CEA-608 is also commonly referred to as “Line 21” or “EIA-608”
The Closed Captioning standard for ATSC digital television worldwide. CEA-708 captions, unlike CEA-608 captions, are not able to be modulated in the vertical blanking interval (VBI) line 21 like a NTSC composite signal and instead are transmitted as digital data.
Also referred to as “OP-47” for HD and “OP-42” for SD. This is a Closed Captioning standard utilized in 50Hz countries. It allows for text and rudimentary graphics to be carried in the vertical blanking interval (VBI) area at the top and bottom of the screen.
Teletext is used to transmit numbered pages of data that can be called up using a remote control, and it is used to transmit Closed Captioning data. Note: “Closed Captioning” and “Subtitles” are commonly used interchangeably in the UK and Ireland.
Ancillary (ANC) data is a means of embedding non-video information, such as audio and metadata, in a serial digital transport stream (SDI). Ancillary data packets are located in the horizontal (HANC) or vertical (VANC) blanking areas of a SDI signal. HANC is primarily used to embed uncompressed audio data in the SDI signal.
VANC is used to embed low-bandwidth data information updated on a per-field or per-frame basis. Closed Caption Data (CCD) and Active Format Description (AFD) are examples of metadata stored as VANC. SMPTE 291M describes the details of Ancillary data packet structures and types.
For HDMI there is no official way to send Closed Captions as metadata in an HDMI signal. In this aspect, any AJA device that can accept SDI or HD-SDI Closed Captions is unable to pass those Closed Captions out of any HDMI port the device may have.
The primary difference between AJA FS Closed Captioning conversion and many other caption converters available is that when converting CEA-608 to CEA-708 captions, FS products fully convert CEA-608 to CEA-708. This ensures that the CEA-708 packets use native syntax which is decodable by all HD television sets. Some SD to HD upconverters only perform the simpler CEA-608 encapsulation operation, which can lead to interoperability problems with HD televisions and equipment that are designed to decode native CEA-708 syntax. For the FS product family, please note the following:
BRIDGE LIVE fully supports both CEA-608 and CEA-708 Closed Captioning for both SDI input and output.
BRIDGE LIVE also enables CEA-608/708 data to be embedded within a H.264/H.265 stream as Supplemental Enhancement Information (SEI) messages.
Closed Captioning is supported on capture via SDI. The HELO Plus encapsulates Closed Caption into SEI messages in the H.264 media and is present on the output stream and viable for use in file based closed captioning workflows. Closed Captioning not supported via HDMI input or output, or the SDI output.
AJA KONA cards, Io devices and T-TAP Pro can be used in either a Retail context for creative artists, or an SDK implementation for software developers. AJA Corvid cards can also be used for SDK implementation for software developers.
Retail usage entails downloading the AJA Desktop Software package, from AJA.com and utilizing the inbuilt driver, AJA applications and integrations with 3rd party applications such as Adobe Premiere Pro, Apple Final Cut Pro, Avid Media Composer and Telestream Wirecast.
SDK implementation means being a signed-up developer using the AJA NTV2 SDK to add video I/O to a software product/project.
There are some differences in capabilities between these two models, whereby the retail support is relatively fixed, but developers have more options at their disposal to implement as they see fit.
KONA cards support one or more of the following:
Closed Captioning Is supported on capture via SDI and is carried to SDI loop outputs. Captioning data is encoded as a QuickTime CC track and viable for use in file-based closed captioning workflows. Captioning data is also recorded as VANC and is visible on playout from the unit.
For files that only contain a QuickTime CC track and no VANC, the QuickTime CC track will be decoded and embedded in the SDI 1 output VANC. Closed captioning not supported via HDMI input or output. Only in single channel mode is captioning supported for ProRes file formats.
Closed Captioning data is recorded as VANC. Note that a QuickTime Closed Caption track is not created. Closed Caption support is included, but playback of captions is only guaranteed for clips generated by Ki Pro Rack and not subsequently modified.
CEA-608 and CEA-708 data is passed through from input to output for the entire range of AJA FiDO (3G and 12G) Mini-Converters.
CEA-608 and CEA-708 data is passed through from input to output for the entire range of AJA KUMO routers (3G and 12G).
The following AJA openGear cards support Closed Captioning data passed from input to output: