Closed Captioning

Introduction

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 before providing a list of AJA products that are Closed Caption compatible.


CEA-608*

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”

CEA-708

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.


Teletext

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.

ANC Packets

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.

Closed Captioning and HDMI

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.

AJA Products Supporting Closed Captioning

Closed Captioning

FS-Series Products and Closed Captioning

AJA produces a range of rack mounted Frame Synchronizers that offer support for Closed Captions. All AJA FS products except the FS-Mini and OG-FS-Mini support conversion between CEA-608 and CEA-708 captions in either direction:

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:

  • CEA-608 (Line 21) to CEA-708 and CEA-708 to CEA-608 conversion is supported on all models
  • CEA-608 and CEA-708 pass-through while performing a wide range of conversions is supported on all models
  • FS-HDR will maintain caption data on HDR to SDR and SDR to HDR conversions
  • Teletext (OP-42/47) captions are preserved when passing through PAL and 625i/50 formats on all models
  • CEA-608 captioning via ANC packets is not supported on any model
  • Conversion between OP-42 and OP-47 is not supported on any model
  • Conversion between OP-42/47 and CEA-608/708 is not supported on any model
  • Capture or output of captioning data via HDMI is not supported on any model as HDMI does not support Closed Captioning data that is not rendered to the frame

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BRIDGE LIVE and Closed Captioning

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.

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HELO Plus and Closed Captioning

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.

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HELO and Closed Captioning

Closed Captioning is supported on capture via SDI and is carried to the SDI loop output. The HELO 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.

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AJA I/O Cards and Devices and Closed Captioning

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.


Physical Transports

KONA cards support one or more of the following:

  • SDI – Caption support via:
    • SMPTE 291 ancillary data
    • “Line 21” (PAL/OP-41, NTSC/EIA-608) embedded in SD video
  • HDMI – No caption support (other than those already rendered in video image)
  • Analog – Caption support limited to “Line 21” (PAL/OP-41, NTSC/EIA-608) embedded in SD video

Firmware Capabilities

  • Normal Video Raster
    • Supported by all NTV2 devices
    • Caption support limited to “Line 21” (PAL/OP-41, NTSC/EIA-608) embedded in SD video
  • Tall-Frames – expands Normal Video Raster to provide VANC lines
    • Supported by all NTV2 devices
    • SD, HD, 2K only (no UltraHD, 4K, UltraHD2, 8K support)
    • Supports captions transported in VANC (e.g. PAL/OP-47, NTSC/CEA608/CEA708, ARIB, TeleText, etc.)
  • Anc Inserters/Extractors – for inserting/extracting any SMPTE 291 ancillary data
    • Supported across KONA 5, KONA 4, KONA 1, but not supported with KONA LHi or KONA LHe Plus. See individual card and device abilities below.
    • Supports captions transported in VANC, including PAL/OP-47, NTSC/CEA-608, NTSC/CEA-708, ARIB, TeleText, etc.
    • Also supports US NTSC (EIA-608) captions via “Line 21” in SD video
    • Some AJA products also support up to UltraHD, 4K (no UltraHD2, 8K support), see individual card and device abilities below.

Individual KONA Card Abilities:

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Io and T-TAP Pro Abilities:

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Individual Corvid Card Abilities:

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Retail Applications

AJA Control Room

  • Caption support currently limited to NTSC only (as provided by NTV2 SDK):
    • Supports CEA-608 or 608-in-708
    • No “native” CEA-708 support
  • Only uses ANC Ins/Ext firmware – no Tall-Frames!
    • Thus, no caption support on KONA LHi, KONA LHe Plus

3rd Party

  • Avid & Adobe Plugins
    • All SMPTE-291 (ANC) based captions supported (pass-through supplied/received caption packets)
    • Adobe Premiere supports native 708 if the raw data is available. For instance in the Adobe plug-ins we handle the case where Premiere hands us full 708 data, we just pass it through to the device.
    • Avid Media Composer supports active video ANC(line 21) or ANC via ANC extractor/inserter (up to UltraHD/4K)
  • Apple FCPX – no caption support
  • Telstream Wirecast – no caption support via SDI I/O

SDK

  • Supports any/all “raw” caption data input/output from/to any NTV2 Hardware based on what the hardware & firmware supports, including PAL/OP-41/47, TeleText, ARIB, NTSC, etc.
  • Additional NTSC Caption support in AJA Ancillary Data Library
    • Encode/decode EIA-608 bytecode pairs to/from SD “Line 21” data obtained by Anc Inserters/Extractors or any video raster
    • Input/output CEA-608 bytecode pairs to/from ancillary data packets obtained by Anc Inserters/Extractors or Tall-Frame rasters
  • Demo Apps
    • NTV2Capture can be configured to capture all ancillary data to a raw data file.
    • NTV2Player can be configured to play back (inject) ancillary data from a previously-recorded raw data file.
    • NTV2CCGrabber decodes and reports/displays incoming NTSC CEA-608 or 608-in-708 (HD) captions.
    • NTV2CCPlayer encodes text files as outgoing NTSC CEA-608 or 608-in-708 (HD) captions.
  • Tools
    • NTV2Watcher
      • Anc Inspector – monitors all incoming/outgoing ancillary data, including “Line 21” (SD), Tall-Frame and/or Anc Inserter/Extractor
      • CEA-608 Caption Encoder/Decoder tool
      • Decodes CEA-608 bytepairs transmitted from Anc Inspector
      • Interactively encodes character sequences into CEA-608 bytepairs, and transmits them to a device frame buffer
      AJA Logger – can monitor and/or record all log messages related to SDK caption encoding/decoding

SDK Extras

  • Additional NTSC Caption support in proprietary AJA Closed-Caption Library (OEM SDK only)
    • Full-featured CEA-608 encoder/decoder
    • Limited-functionality CEA-708 encoder/decoder only supports embedded 608-in-708
    • High-quality CEA-608 caption renderer
      • Supports all regions (including Europe)
      • Unicode-compliant
      • Supports most NTV2 frame buffer geometries and pixel formats
  • No additional non-U.S. caption support (e.g. codecs for Teletext, PAL/OP-41/47, ARIB, etc.)

Additional Notes / Clarifications:

  • Conversion between 608 and 708 could be done using the SDK proprietary caption library's 608 to 708 translator class – but it is a software developer task to use it.
  • OP41 PAL SD closed caption encoding/decoding and rendering could be implemented by a developer using our SDK.
  • Conversion between OP-42 and OP-47 can be done using our hardware and SDK, but it is incumbent on the Developer Partner to write the software to perform the conversion.
  • Caption pass-through is supported in E-E mode (on devices having inputs and outputs), but CSC/LUTs in path could cause issues.
  • Caption data is maintained when signaling HDR via SDI

Ki Pro Ultra 12G and Closed Captioning

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.

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Ki Pro Rack and Closed Captioning

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.

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FiDO Optical Fiber Converters and Closed Captioning

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.

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SDI DA mini-converters and Closed Captioning

CEA-608 and CEA-708 data is passed through from input to output for the entire range of AJA SDI DA mini-converters.

12GDA 3GDA


KUMO Routers and Closed Captioning

CEA-608 and CEA-708 data is passed through from input to output for the entire range of AJA KUMO routers (3G and 12G).

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openGear Cards and Closed Captioning

The following AJA openGear cards support Closed Captioning data passed from input to output: