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FCC Part 15 Radio Frequency Devices
Section 15.122

The Federal Communications Commission (FCC) is the authority in the United States of America that creates and enforces the use of airwaves throughout the entire radio frequency spectrum. This group of documents contains the entirety of the FCC Part 15 regulations that concern unlicensed radio frequency devices. As with all government documents, this material is in the public domain and may be freely copied so long as the content is not changed. This copy is provided as a convenience for RF Cafe visitors. 

Click here for the Table of Contents.
[Code of Federal Regulations]
[Title 47, Volume 1]
[Revised as of October 1, 2008]
From the U.S. Government Printing Office via GPO Access
[CITE: 47CFR15.122]
[Page 790-799]
 
                       TITLE 47--TELECOMMUNICATION
 
              CHAPTER I--FEDERAL COMMUNICATIONS COMMISSION
 
PART 15_RADIO FREQUENCY DEVICES--Table of Contents
 
                    Subpart B_Unintentional Radiators
 
Sec. 15.122  Closed caption decoder requirements for digital 
television receivers and converter boxes.
    (a)(1) Effective July 1, 2002, all digital television receivers with 
picture screens in the 4:3 aspect ratio with picture screens measuring 
13 inches or larger diagonally, all digital television receivers with 
picture screens in the 16:9 aspect ratio measuring 7.8 inches or larger 
vertically and all separately sold DTV tuners shipped in interstate 
commerce or manufactured in the United States shall comply with the 
provisions of this section.
    Note to paragraph (a)(1): This paragraph places no restrictions on 
the shipping or sale of digital television receivers that were 
manufactured before July 1, 2002.
    (2) Effective July 1, 2002, DTV converter boxes that allow digitally 
transmitted television signals to be displayed on analog receivers shall 
pass available analog caption information to the attached receiver in a 
form recognizable by that receiver's built-in caption decoder circuitry.
    Note to paragraph (a)(2): This paragraph places no restrictions on 
the shipping or sale of DTV converter boxes that were manufactured 
before July 1, 2002.
    (b) Digital television receivers and tuners must be capable of 
decoding closed captioning information that is delivered pursuant to 
EIA-708-B: ``Digital Television (DTV) Closed Captioning'' (incorporated 
by reference, see Sec. 15.38).
    (c) Services. (1) Decoders must be capable of decoding and 
processing data for the six standard services, Caption Service 
1 through Caption Service 6.
    (2) Decoders that rely on Program and System Information Protocol 
data to implement closed captioning functions must be capable of 
decoding and processing the Caption Service Directory data. Such 
decoders must be capable of decoding all Caption Channel Block Headers 
consisting of Standard Service Headers, Extended Service Block Headers, 
and Null Block headers. However, decoding of the data is required only 
for Standard Service Blocks (Service IDs <-6), and then only if the 
characters for the corresponding language are supported. The decoders 
must be able to display the directory for services 1 through 6.
    (d) Code space organization. (1) Decoders must support Code Space 
C0, G0, C1, and G1 in their entirety.
[[Page 791]]
[GRAPHIC] [TIFF OMITTED] TR29SE00.000
    (2) The following characters within code space G2 must be supported:
    (i) Transparent space (TSP).
    (ii) Non-breaking transparent space (NBTSP).
    (iii) Solid block ( ).
    (iv) Trademark symbol (\TM\).
    (v) Latin-1 characters [Scaron], [OElig], [scaron], [oelig], [Yuml].
    (3) The substitutions in Table 2 are to be made if a decoder does 
not support the remaining G2 characters.
                Table 2--G2 Character Substitution Table
------------------------------------------------------------------------
           G2 Character                       Substitute with
------------------------------------------------------------------------
Open single quote (`), G2 char     G0 single quote (`), char code 0x27
 code 0x31.
Close single quote ('), G2 char    G0 single quote ('), char code 0x27
 code 0x32.
Open double quote (``), G2 char    G0 double quote (``), char code 0x22
 code 0x33.
Close double quote (''), G2 char   G0 double quote (''), char code 0x22
 code 0x34.
Bold bullet (),  G1 bullet (), char
 G2 char code 0x35.                 code 0xB7
Elipsis (. . .), G2 char code      G0 underscore (--), char code 0x5F
 0x25.
One-eighth (\1/8\), G2 char code   G0 percent sign (%), char code 0x25
 0x76.
Three-eighths (\3/8\), G2 char     G0 percent sign (%), char code 0x25
 code 0x77.
Five-eighths (\5/8\), G2 char      G0 percent sign (%), char code 0x25
 code 0x78.
Seven-eighths (\7/8\), G2 char     G0 percent sign (%), char code 0x25
 code 0x79.
[[Page 792]]
Vertical border ([verbar]), G2     G0 stroke ([verbar]), char code 0x7C
 char code 0x7A.
Upper-right border ([rceil]), G2   G0 dash (-), char code 0x2D
 char code 0x7B.
Lower-left border ([lfloor]), G2   G0 dash (-), char code 0x2D
 char code 0x7C.
Horizontal border ([horbar]), G2   G0 dash (-), char code 0x2D
 char code 0x7D.
Lower-right border ([rfloor]), G2  G0 dash (-), char code 0x2D
 char code 0x7E.
Upper-left border ([lceil]), G2    G0 dash (-), char code 0x2D
 char code 0x7F.
------------------------------------------------------------------------
    (4) Support for code spaces C2, C3, and G3 is optional. All 
unsupported graphic symbols in the G3 code space are to be substituted 
with the G0 underscore character (--), char code 0x5F.
    (e) Screen coordinates. Table 3 specifies the screen coordinate 
resolutions and limits for anchor point positioning in 4:3 and 16:9 
display formats, and the number of characters per row.
                                Table 3--Screen Coordinate Resolutions and Limits
----------------------------------------------------------------------------------------------------------------
                                                                                           Maximum     Maximum
     Screen aspect ratio         Maximum anchor position      Minimum anchor position     displayed   characters
                                        resolution                   resolution             rows       per row
----------------------------------------------------------------------------------------------------------------
4:3..........................  75vx160h...................  15vx32h....................           4           32
16:9.........................  75vx210h...................  15vx42h....................           4           42
Other........................  75vx(5xH)..................  15vxH*.....................           4          \1\
----------------------------------------------------------------------------------------------------------------
\1\H = 32 x (the width of the screen in relation to a 4:3 display). For example, the 16:9 format is \1/3\ wider
  than a 4:3 display; thus, H = 32 * \4/3\ = 42.667, or 42.
    (1) This means that the minimum grid resolution for a 4:3 aspect 
ratio instrument is 15 vertical positions x 32 horizontal positions. 
This minimum grid resolution for 16:9 ratio instrument is 15 vertical 
positions x 42 horizontal positions. These minimum grid sizes are to 
cover the entire safe-title area of the corresponding screen.
    (2) The minimum coordinates equate to a \1/5\ reduction in the 
maximum horizontal and vertical grid resolution coordinates. Caption 
providers are to use the maximum coordinate system values when 
specifying anchor point positions. Decoders using the minimum resolution 
are to divide the provided horizontal and vertical screen coordinates by 
5 to derive the equivalent minimum coordinates.
    (3) Any caption targeted for both 4:3 and 16:9 instruments is 
limited to 32 contiguous characters per row. If a caption is received by 
a 4:3 instrument that is targeted for a 16:9 display only, or requires a 
window width greater than 32 characters, then the caption may be 
completely disregarded by the decoder. 16:9 instruments should be able 
to process and display captions intended for 4:3 displays, providing all 
other minimum recommendations are met.
    (4) If the resulting size of any window is larger than the safe 
title area for the corresponding display's aspect ratio, then this 
window will be completely disregarded.
    (f) Caption windows. (1) Decoders need to display no more than 4 
rows of captions on the screen at any given time, regardless of the 
number of windows displayed. This implies that no more than 4 windows 
can be displayed at any given time (with each having only one caption 
row). However, decoders should maintain storage to support a minimum 
total of 8 rows of captions. This storage is needed for the worst-case 
support of a displayed window with 4 rows of captioning and a non-
displayed window which is buffering the incoming rows for the next 4-row 
caption. As implied above, the maximum number of windows that may be 
displayed at any one time by a minimum decoder implementation is 4. If 
more than 4 windows are defined in the caption stream, the decoder may 
disregard the youngest and lowest priority window definition(s). Caption 
providers must be aware of this limitation, and either restrict the 
total number of windows used or accept that some windows will not be 
displayed.
[[Page 793]]
 
    (2) Decoders do not need to support overlapped windows. If a window 
overlaps another window, the overlapped window need not be displayed by 
the decoder.
    (3) At a minimum, decoders will assume that all windows have rows 
and columns ``locked''. This implies that if a decoder implements the 
SMALL pen-size, then word-``un''wrapping, when shrinking captions, need 
not be implemented. Also, if a decoder implements the LARGE pen size, 
then word wrapping (when enlarging captions) need not be implemented.
    (4) Whenever possible, the receiver should render embedded carriage 
returns as line breaks, since these carriage returns indicate an 
important aspect of the caption's formatting as determined by the 
service provider. However, it may sometimes be necessary for the 
receiver to ignore embedded line breaks. For example, if a caption is to 
appear in a larger font, and if its window's rows and/or columns are 
unlocked, the rows of text may need to become longer or shorter to fit 
within the allocated space. Such automatic reformatting of a caption is 
known as ``word wrap.'' If decoders support word-wrapping, it must be 
implemented as follows:
    (i) The receiver should follow standard typographic practice when 
implementing word wrap. Potential breaking points (word-wrapping points) 
are indicated by the space character (20h) and by the hyphen character 
(2Dh).
    (ii) If a row is to be broken at a space, the receiver should remove 
the space from the caption display. If a row is to be broken after a 
hyphen, the hyphen should be retained.
    (iii) If an embedded return is to be removed, it should usually be 
replaced with a space. However, if the character to the left of the 
embedded return is a hyphen, the embedded return should be removed but 
NOT replaced with a space.
    (iv) This specification does not include optional hyphens, nor does 
it provide for any form of automatic hyphenation. No non-breaking hyphen 
is defined. The non-breaking space (A0h in the G1 code set) and the non-
breaking transparent space (21h in the G2 code set) should not be 
considered as potential line breaks.
    (v) If a single word exceeds the length of a row, the word should be 
placed at the start of a new row, broken at the character following the 
last character that fits on the row, and continued with further breaks 
if needed.
    (g) Window text painting. (1) All decoders should implement 
``left'', ``right'', and ``center'' caption-text justification. 
Implementation of ``full'' justification is optional. If ``full'' 
justification is not implemented, fully justified captions should be 
treated as though they are ``left'' justified.
    (i) For ``left'' justification, decoders should display any portion 
of a received row of text when it is received. For ``center'', 
``right'', and ``full'' justification, decoders may display any portion 
of a received row of text when it is received, or may delay display of a 
received row of text until reception of a row completion indicator. A 
row completion indicator is defined as receipt of a CR, ETX or any other 
command, except SetPenColor, SetPenAttributes, or SetPenLocation where 
the pen relocation is within the same row.
    (ii) Receipt of a character for a displayed row which already 
contains text with ``center'', ``right'' or ``full'' justification will 
cause the row to be cleared prior to the display of the newly received 
character and any subsequent characters. Receipt of a justification 
command which changes the last received justification for a given window 
will cause the window to be cleared.
    (2) At a minimum, decoders must support LEFT--TO--RIGHT printing.
    (3) At a minimum, decoders must support BOTTOM--TO--TOP scrolling. 
For windows sharing the same horizontal scan lines on the display, 
scrolling may be disabled.
    (4) At a minimum, decoders must support the same recommended 
practices for scroll rate as is provided for NTSC closed-captioning.
    (5) At a minimum, decoders must support the same recommended 
practices for smooth scrolling as is provided for NTSC closed-
captioning.
[[Page 794]]
    (6) At a minimum, decoders must implement the ``snap'' window 
display effect. If the window ``fade'' and ``wipe'' effects are not 
implemented, then the decoder will ``snap'' all windows when they are to 
be displayed, and the ``effect speed'' parameter is ignored.
    (h) Window colors and borders. At a minimum, decoders must implement 
borderless windows with solid, black backgrounds (i.e., border type = 
NONE, fill color = (0,0,0), fill opacity = SOLID), and borderless 
transparent windows (i.e., border type = NONE, fill opacity = 
TRANSPARENT).
    (i) Predefined window and pen styles. Predefined Window Style and 
Pen Style ID's may be provided in the DefineWindow command. At a 
minimum, decoders should implement Predefined Window Attribute Style 1 
and Predefined Pen Attribute Style 1, as shown in Table 4 and Table 5, 
respectively.
[[Page 795]]

                                                                              Table 4--Predefined Window Style ID's
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
                                                 Print          Scroll       Word      Display       Effect        Effect                      Fill                     Border
      Style ID           Justify      direction      direction      wrap      effect       direction      speed      Fill color     opacity    Border type     color          Usage
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
1............................  Left........  Left-to-right  Bottom-to-top  No.....  Snap........  n/a.........  n/a........  (0,0,0)       Solid......  None.......  n/a........  NTSC Style
                                                                                                                              Black.                                               PopUp
                                                                                                                                                                                   Captions
2............................  Left........  Left-to-right  Bottom-to-top  No.....  Snap........  n/a.........  n/a........  n/a.........  Transparent  None.......  n/a........  PopUp Captions
                                                                                                                                                                                   w/o Black
                                                                                                                                                                                   Background
3............................  Cntr........  Left-to-right  Bottom-to-top  No.....  Snap........  n/a.........  n/a........  (0,0,0)       Solid......  None.......  n/a........  NTSC Style
                                                                                                                              Black.                                               Centered
                                                                                                                                                                                   PopUp
                                                                                                                                                                                   Captions
4............................  Left........  Left-to-right  Bottom-to-top  Yes....  Snap........  n/a.........  n/a........  (0,0,0)       Solid......  None.......  n/a........  NTSC Style
                                                                                                                              Black.                                               RollUp
                                                                                                                                                                                   Captions
5............................  Left........  Left-to-right  Bottom-to-top  Yes....  Snap........  n/a.........  n/a........  n/a.........  Transparent  None.......  n/a........  RollUp
                                                                                                                                                                                   Captions w/o
                                                                                                                                                                                   Black
                                                                                                                                                                                   Background
6............................  Cntr........  Left-to-right  Bottom-to-top  Yes....  Snap........  n/a.........  n/a........  (0,0,0)       Solid......  None.......  n/a........  NTSC Style
                                                                                                                              Black.                                               Centered
                                                                                                                                                                                   RollUp
                                                                                                                                                                                   Captions
7............................  Left........  Top-to-bottom  Right-to-left  No.....  Snap........  n/a.........  n/a........  (0,0,0)       Solid......  None.......  n/a........  Ticker Tape
                                                                                                                              Black.
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                               Table 5--Predefined Pen Style ID's
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                                                     Foregrnd     Foregrnd     Backgrnd     Backgrnd
      Predefined style ID          Pen size      Font style       Offset      Italics     Underline    Edge type      color       opacity       color       opacity     Edge color      Usage
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
1.............................  Stndr........  0............  Normal.......  No.......  No..........  None.......  (2,2,2)      Solid......  (0,0,0)      Solid......  n/a........  Default NTSC
                                                                                                                    White.                    Black.                                 Style*
[[Page 796]]
2.............................  Stndr........  1............  Normal.......  No.......  No..........  None.......  (2,2,2)....  Solid......  (0,0,0)      Solid......  n/a........  NTSC Style*
                                                                                                                                              White.                                 Mono w/
                                                                                                                                                                                     Serif
3.............................  Stndr........  2............  Normal.......  No.......  No..........  None.......  (2,2,2)      Solid......  (0,0,0)      Solid......  n/a........  NTSC Style*
                                                                                                                    White.                    Black.                                 Prop w/
                                                                                                                                                                                     Serif
4.............................  Stndr........  3............  Normal.......  No.......  No..........  None.......  (2,2,2)      Solid......  (0,0,0)      Solid......  n/a........  NTSC Style*
                                                                                                                    White.                    Black.                                 Mono w/o
                                                                                                                                                                                     Serif
5.............................  Stndr........  4............  Normal.......  No.......  No..........  None.......  (2,2,2)      Solid......  (0,0,0)      Solid......  n/a........  NTSC Style*
                                                                                                                    White.                    Black.                                 Prop w/o
                                                                                                                                                                                     Serif
6.............................  Stndr........  3............  Normal.......  No.......  No..........  Unifrm.....  (2,2,2)      Solid......  n/a........  Transparent  (0,0,0)      Mono w/o
                                                                                                                    White.                                              Black.       Serif,
                                                                                                                                                                                     Bordered
                                                                                                                                                                                     Text, No BG
7.............................  Stndr........  4............  Normal.......  No.......  No..........  Unifrm.....  (2,2,2)      Solid......  n/a........  Transparent  (0,0,0)      Prop. w/o
                                                                                                                    White.                                              Black.       Serif,
                                                                                                                                                                                     Bordered
                                                                                                                                                                                     Text, No BG
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
*``NTSC Style''--White Text on Black Background
[[Page 797]]
    (j) Pen size. (1) Decoders must support the standard, large, and 
small pen sizes and must allow the caption provider to choose a pen size 
and allow the viewer to choose an alternative size. The STANDARD pen 
size should be implemented such that the height of the tallest character 
in any implemented font is no taller than \1/15\ of the height of the 
safe-title area, and the width of the widest character is no wider than 
\1/32\ of the width of the safe-title area for 4:3 displays and \1/42\ 
of the safe-title area width for 16:9 displays.
    (2) The LARGE pen size should be implemented such that the width of 
the widest character in any implemented font is no wider than \1/32\ of 
the safe-title area for 16:9 displays. This recommendation allows for 
captions to grow to a LARGE pen size without having to reformat the 
caption since no caption will have more than 32 characters per row.
    (k) Font styles. (1) Decoders must support the eight fonts listed 
below. Caption providers may specify 1 of these 8 font styles to be used 
to write caption text. The styles specified in the ``font style'' 
parameter of the SetPenAttributes command are numbered from 0 through 7. 
The following is a list of the 8 required font styles. For information 
purposes only, each font style references one or more popular fonts 
which embody the characteristics of the style:
    (i) 0--Default (undefined)
    (ii) 1--Monospaced with serifs (similar to Courier)
    (iii) 2--Proportionally spaced with serifs (similar to Times New 
Roman)
    (iv) 3--Monospaced without serifs (similar to Helvetica Monospaced)
    (v) 4--Proportionally spaced without serifs (similar to Arial and 
Swiss)
    (vi) 5--Casual font type (similar to Dom and Impress)
    (vii) 6--Cursive font type (similar to Coronet and Marigold)
    (viii) 7--Small capitals (similar to Engravers Gothic)
    (2) Font styles may be implemented in any typeface which the decoder 
manufacturer deems to be a readable rendition of the font style, and 
need not be in the exact typefaces given in the example above. Decoders 
must include the ability for consumers to choose among the eight fonts. 
The decoder must display the font chosen by the caption provider unless 
the viewer chooses a different font.
    (l) Character offsetting. Decoders need not implement the character 
offsetting (i.e., subscript and superscript) pen attributes.
    (m) Pen styles. At a minimum, decoders must implement normal, 
italic, and underline pen styles.
    (n) Foreground color and opacity. (1) At a minimum, decoders must 
implement transparent, translucent, solid and flashing character 
foreground type attributes.
    (2) At a minimum, decoders must implement the following character 
foreground colors: white, black, red, green, blue, yellow, magenta and 
cyan.
    (3) Caption providers may specify the color/opacity. Decoders must 
include the ability for consumers to choose among the color/opacity 
options. The decoder must display the color/opacity chosen by the 
caption provider unless the viewer chooses otherwise.
    (o) Background color and opacity. (1) Decoders must implement the 
following background colors: white, black, red, green, blue, yellow, 
magenta and cyan. It is recommended that this background is extended 
beyond the character foreground to a degree that the foreground is 
separated from the underlying video by a sufficient number of background 
pixels to insure the foreground is separated from the background.
    (2) Decoders must implement transparent, translucent, solid and 
flashing background type attributes. Caption providers may specify the 
color/opacity. Decoders must include the ability for consumers to choose 
among the color/opacity options. The decoder must display the color/
opacity chosen by the caption provider unless the viewer chooses 
otherwise.
    (p) Character edges. Decoders must implement separate edge color and 
type attribute control.
    (q) Color representation. (1) At a minimum, decoders must support 
the 8 colors listed in Table 6.
[[Page 798]]

                    Table 6--Minimum Color List Table
------------------------------------------------------------------------
                    Color                        Red     Green     Blue
------------------------------------------------------------------------
Black........................................        0        0        0
White........................................        2        2        2
Red..........................................        2        0        0
Green........................................        0        2        0
Blue.........................................        0        0        2
Yellow.......................................        2        2        0
Magenta......................................        2        0        2
Cyan.........................................        0        2        2
------------------------------------------------------------------------
    (2)(i) When a decoder supporting this Minimum Color List receives an 
RGB value not in the list, it will map the received value to one of the 
values in the list via the following algorithm:
    (A) All one (1) values are to be changed to 0.
    (B) All two (2) values are to remain unchanged.
    (C) All three (3) values are to be changed to 2.
    (ii) For example, the RGB value (1,2,3) will be mapped to (0,2,2), 
(3,3,3) will be mapped to (2,2,2) and (1,1,1) will be mapped to (0,0,0).
    (3) Table 7 is an alternative minimum color list table supporting 22 
colors.
              Table 7--Alternative Minimum Color List Table
------------------------------------------------------------------------
                    Color                        Red     Green     Blue
------------------------------------------------------------------------
Black........................................        0        0        0
Gray.........................................        1        1        1
White........................................        2        2        2
Bright White.................................        3        3        3
Dark Red.....................................        1        0        0
Red..........................................        2        0        0
Bright Red...................................        3        0        0
Dark Green...................................        0        1        0
Green........................................        0        2        0
Bright Green.................................        0        3        0
Dark Blue....................................        0        0        1
Blue.........................................        0        0        2
Bright Blue..................................        0        0        3
Dark Yellow..................................        1        1        0
Yellow.......................................        2        2        0
Bright Yellow................................        3        3        0
Dark Magenta.................................        1        0        1
Magenta......................................        2        0        2
Bright Magenta...............................        3        0        3
Dark Cyan....................................        0        1        1
Cyan.........................................        0        2        2
Bright Cyan..................................        0        3        3
------------------------------------------------------------------------
    (i) When a decoder supporting the Alternative Minimum Color List in 
Table 7 receives an RGB value not in the list (i.e., an RGB value whose 
non-zero elements are not the same value), it will map the received 
value to one of the values in the list via the following algorithm:
    (A) For RGB values with all elements non-zero and different--e.g., 
(1,2,3), (3,2,1), and (2,1,3), the 1 value will be changed to 0, the 2 
value will remain unchanged, and the 3 value will be changed to 2.
    (B) For RGB values with all elements non-zero and with two common 
elements--e.g. (3,1,3), (2,1,2), and (2,2,3), if the common elements are 
3 and the uncommon one is 1, then the 1 elements is changed to 0; e.g. 
(3,1,3) [rarr] (3,0,3). If the common elements are 1 and the uncommon 
element is 3, then the 1 elements are changed to 0, and the 3 element is 
changed to 2; e.g. (1,3,1) [rarr] (0,2,0). In all other cases, the 
uncommon element is changed to the common value; e.g., (2,2,3) [rarr] 
(2,2,2), (1,2,1) [rarr] (1,1,1), and (3,2,3) [rarr] (3,3,3).
    (ii) All decoders not supporting either one of the two color lists 
described above, must support the full 64 possible RGB color value 
combinations.
    (r) Character rendition considerations. In NTSC Closed Captioning, 
decoders were required to insert leading and trailing spaces on each 
caption row. There were two reasons for this requirement:
    (1) To provide a buffer so that the first and last characters of a 
caption row do not fall outside the safe title area, and
    (2) To provide a black border on each side of a character so that 
the ``white'' leading pixels of the first character on a row and the 
trailing ``white'' pixels of the last character on a row do not bleed 
into the underlying video.
    (i) Since caption windows are required to reside in the safe title 
area of the DTV screen, reason 1 (above) is not applicable to DTVCC 
captions.
    (ii) The attributes available in the SetPenAttributes command for 
character rendition (e.g., character background and edge attributes) 
provide unlimited flexibility to the caption provider when describing 
caption text in an ideal decoder implementation. However, manufacturers 
need not implement all pen attributes. Thus it is recommended that no 
matter what the level of implementation, decoder manufacturers should 
take into account the readability of all caption text against a variety 
of all video backgrounds, and should implement some
[[Page 799]]
automatic character delineation when the individual control of character 
foreground, background and edge is not supported.
    (s) Service synchronization. Service Input Buffers must be at least 
128 bytes in size. Caption providers must keep this lower limit in mind 
when following Delay commands with other commands and window text. In 
other words, no more than 128 bytes of DTVCC commands and text should be 
transmitted (encoded) before a pending Delay command's delay interval 
expires.
    (t) Settings. Decoders must include an option that permits a viewer 
to choose a setting that will display captions as intended by the 
caption provider (a default). Decoders must also include an option that 
allows a viewer's chosen settings to remain until the viewer chooses to 
alter these settings, including periods when the television is turned 
off.
[65 FR 58471, Sept. 29, 2000, as amended at 69 FR 2849, Jan. 21, 2004]





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