Closed Captioning for Broadcast Television: What’s the Difference Between 708 Captions and 608 (Line 21) Captions?
There are two standards of closed captions for broadcast television. CEA-608 captions (also known as Line 21 captions and EIA-608 captions) were the old standard for closed captioning of analog television. CEA-708 captions (also known as EIA-708 captions) are the new standard for closed captioning of digital television.
Since digital television officially replaced analog television in the United States in 2009, most captions have been transitioned over from 608 to 708. However, in an effort to make the transition smoother, digital television does support 608 captions, while analog television does not support 708 captions. These days, 708 captions are the preferred option, and are considered standard by the FCC.
Comparison of 608 (Line 21) Captions and 708 Captions
608 and 708 captions have numerous differences. 708 captions are an improved captioning standard, with more options for appearance, placement, and languages. The two standards differ in major ways, as outlined in the following chart. Below that, you’ll find more detailed information on each standard.
CEA-608 (Line 21) vs. CEA-708 Caption Comparison CEA-608 (Line 21) Captions CEA-708 Captions Standard for analog television Standard for digital television Can be transmitted on analog & digital television Can only be transmitted on digital television Appearance: Uppercase white text on black box background Appearance: User can control caption appearance. Options include: 8 fonts in 3 sizes, 64 text colors, 64 background colors, background opacity, and edged or dropshadowed text Supports up to 2 languages at a time Supports multilingual captions Language options are limited to English, Spanish, French, Portuguese, Italian, German, and Dutch (due to lack of special characters) Supports captions in any language (characters & symbols from every alphabet are supported) Transmitted on Line 21 Embedded in MPEG-2 streams Caption position is fixed. Caption position can be changed. The FCC requires that captions be repositioned if they obscure important visual information.
CEA-608 Captions (Line 21 Captions)
608 captions used to be the standard for analog broadcast television. While they have mainly been replaced by 708 captions, 608 captions can be embedded in digital television. You are probably familiar with their stereotypical appearance: black box backgrounds with all uppercase white text.
608 captions are hidden in the Line 21 data area (hence the name) of the analog television signal and are only viewable with a decoder. Line 21 has two fields; most often, English captions are transmitted in the first field and Spanish captions or captions meant for children are transmitted in the second field. Digital television does support 608 captions in its picture user data (this was meant to make the transition easier when digital television replaced analog television). However, 608 captions do not support any of the appearance options that 708 captions have, and do not fit with many of the FCC’s current requirements.
Because of character limitations, 608 captions are limited to encoding in English, Spanish, French, Portuguese, Italian, German, & Dutch. Further, the two fields available in Line 21 allow for only two language options at a time.
608 captions have a fixed position on the screen. Note that this is not compliant with the FCC’s quality standards, introduced in February of 2014.
About CEA-708 Captions
CEA-708 captions, which were introduced for use with digital television, follow much more advanced standards than 608 captions. These captions provide user control options for appearance, allowing the viewer to select from 8 font options, 3 text sizes, 64 text colors, and 64 background colors. 708 captions also have options for background opacity and dropshadowed or edged text. All of these options make 708 captions more accessible to individual viewers with unique requirements and preferences. 708 captions can be either roll-up or pop-on; this is the only appearance-related quality that the user cannot control, as roll-up and pop-on captions are formatted differently.
708 captions go into MPEG-2 streams in the picture user data of digital television. Captions are transmitted in picture order and must be rearranged like picture frames. This is known as the DTVCC transport stream. It is possible to transmit 608 captions on digital television, but it is not possible to stream 708 captions on analog television.
708 captions have a complete library of special characters and symbols and are designed to support any alphabet in the world. Further, the way in which 708 captions are transmitted allows for multiple tracks for one program. The multilingual capability of 708 captions makes programming much more accessible to a global audience.
708 captions do not have to be fixed in one position, as 608 captions do. The FCC’s quality standards state that captions should not block other important on-screen information. 708 captions can be repositioned to comply with the FCC’s standards, whereas 608 captions cannot.
The Future of 608 vs 708 Closed Captions
While 608 captions still appear on digital television, it is clear that the standards are moving away from this outdated format. 608 captions are not compliant with most of the FCC’s recent rules and standards, and have little place in broadcast programming moving forward. It is also worth noting that many online video captioning standards – most notably user control requirements – are based off of CEA-708 standards.
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