Digital television interoperability issues Closed captioning

1 digital television interoperability issues

1.1 americas

1.1.1 incompatibility issues digital tv


1.2 uk/australia
1.3 new zealand
1.4 digital television standard captioning improvements

digital television interoperability issues
americas

the atsc digital television system specified 2 different kinds of closed captioning datastream standards: original analog-compatible (available line 21) , more modern digital-only cea-708 formats delivered within video stream. fcc mandates broadcasters deliver (and generate, if necessary) both datastream formats cea-708 format merely conversion of line 21 format. canadian crtc has not mandated broadcasters either broadcast both datastream formats or exclusively in 1 format. broadcasters , networks avoid large conversion cost outlays provide eia-608 captions along transcoded cea-708 version encapsulated within cea-708 packets.

incompatibility issues digital tv

many viewers find when acquire digital television or set-top box unable view closed caption (cc) information, though broadcaster sending , tv able display it.

originally, cc information included in picture ( line 21 ) via composite video input, there no equivalent capability in digital video interconnects (such dvi , hdmi) between display , source . source , in case, can dvd player or terrestrial or cable digital television receiver. when cc information encoded in mpeg-2 data stream, device decodes mpeg-2 data (a source) has access closed caption information; there no standard transmitting cc information display monitor separately. thus, if there cc information, source device needs overlay cc information on picture prior transmitting display on interconnect s video output.

many source devices not have ability overlay cc information, controlling cc overlay can complicated. example, motorola dct-5xxx , -6xxx cable set-top receivers have ability decode cc information located on mpeg-2 stream , overlay on picture, turning cc on , off requires turning off unit , going special setup menu (it not on standard configuration menu , cannot controlled using remote). historically, dvd players, vcrs , set-top tuners did not need overlaying, since passed information on tv, , not mandated perform overlaying.

many modern digital television receivers can directly connected cables, cannot receive scrambled channels user paying for. thus, lack of standard way of sending cc information between components, along lack of mandate add information picture, results in cc being unavailable many hard-of-hearing , deaf users.

uk/australia

the ebu ceefax-based teletext systems source closed captioning signals, when teletext embedded dvb-t or dvb-s closed captioning signal included. however, dvb-t , dvb-s, not necessary teletext page signal present (itv1, example, not carry analogue teletext signals on sky digital, carry embedded version, accessible services menu of receiver, or more turning them off/on mini menu accessible button).

new zealand

in new zealand, captions use ebu ceefax-based teletext system on dvb broadcasts via satellite , cable television exception of mediaworks new zealand channels switched dvb rle subtitles in 2012 on both freeview satellite , uhf broadcasts, decision made based on tvnz practice of using format on dvb uhf broadcasts (aka freeview hd). made composite video connected tvs incapable of decoding captions on own. also, these pre-rendered subtitles use classic caption style opaque backgrounds overly large font size , obscure picture more more modern, partially transparent backgrounds.

digital television standard captioning improvements

the cea-708 specification provides dramatically improved captioning

an enhanced character set more accented letters , non-latin letters, , more special symbols
viewer-adjustable text size (called caption volume control in specification), allowing individuals adjust tvs display small, normal, or large captions
more text , background colors, including both transparent , translucent backgrounds optionally replace big black block
more text styles, including edged or drop shadowed text rather letters on solid background
more text fonts, including monospaced , proportional spaced, serif , sans-serif, , playful cursive fonts
higher bandwidth, allow more data per minute of video
more language channels, allow encoding of more independent caption streams

as of 2009, however, closed captioning digital television environments done using tools designed analog captioning (working cea-608 ntsc specification rather cea-708 atsc specification). captions run through transcoders made companies eeg enterprises or evertz, convert analog line 21 caption format digital format. means none of cea-708 features used unless contained in cea-608.