CEA-608/708 closed captions are defined in specifications CEA-608 (also known as EIA-608 or Line 21) and CEA-708 (also known as CTA-708). These types of subtitles are generally only used in north America.

Closed captions are not visible in the video. The receiving device must decode the CEA-608/708 stream and overlay the subtitles/closed captions over the video.

CEA-608 is the older specification which was defined in approx. 1973 for 525i5994 SD NTSC video.

CEA-708 was defined for HD and it defines a new closed caption format (708). It also includes the definition how to transport embedded CEA-608 captions within CEA-708 transport modes for backwards compatibility.

When considering transmission of closed captions keep in mind that CEA-608 is a very old specification and contains important limitations like maximum 32 characters per subtitle line and transmission speed of 2 bytes per TV field. CEA-708 is more modern and supports up to 42 characters per subtitle line, however it should be checked that the receiving device can properly receive and display captions according to CEA-708 spec.

Transport of CEA-608/708 Closed Captions

• In SD-SDI CEA-608 is transported within the VBI part of the SDI. FAB can insert such captions into SD-SDI using the FAB FT-HT 14 PCIe card.
• In HD/3G-SDI CEA-608/708 is transported within VANC part of SDI. FAB can insert such captions into HD/3G-SDI using the FAB FT-HT 14 PCIe card.
• In digital video transmission over satellite CEA-608/708 is embedded within the video PID. Therefore the video encoder must provide a way to receive closed captions from SDI or over network to include them withing the video PID.

FAB Solutions for CEA-608/708 Closed Captions

The following FAB solutions can be used for CEA-608/708 closed captions:

• Insertion into SDI with FAB SDI PCIe Card
• Export of closed captions to .SCC file

1. Insertion into SDI with FAB SDI PCIe Card

Closed captions can be inserted in SD 625i50 video in VBI line 22 or in VBI line 18 or in VANC by using FAB Subtitler PRO/LIVE/MPEG/BCAST/XCD with the FAB SDI PCIe Card. For SD 525i59.97 closed captions can be inserted in VBI line 21 or in VANC. For HD-SDI signals closed captions are inserted in VANC as native CEA-708 and also as CEA-608 embedded in CEA-708.

2. Export of closed captions to .SCC file

FAB Subtitler STD/PRO/LIVE/MPEG can open subtitle files in many different formats and convert them to a .SCC file. Automatic conversion of subtitle files to SCC files using a watchfolder is available in FAB Subtitler PRO/LIVE. A HTTP REST interface for external control of file conversion is available in FAB Subtitler MPEG.