TELECOM Digest OnLine - Sorted: Re: Closed captioning (was How is Weather Channel Data....)

Re: Closed captioning (was How is Weather Channel Data....)

Dave Thompson (
Mon, 16 May 2005 04:35:50 GMT

On Wed, 04 May 2005 22:37:17 -0500, Neal McLain
<> wrote:

> PAT wrote:

>> [TELECOM Digest Editor's Note: Regards closed caption, since I
>> sometimes these days do not hear as well as I would like, I
>> frequently leave closed caption turned on (it is an on/off
>> option on my television set) even though I am also using sound
>> as well (closed caption allows me to keep up with words I miss

My hearing is OK (so far) but I also started leaving CC on for some
scifi programs especially to get spellings of names that aren't always
clear from the sound. And I found some interesting things:

>> or do not understand occassionally.) But has anyone else
>> noticed how they really _blow it bad_ sometimes, with trash
>> symbols instead of the words, etc,...

> The "trash symbols" you see are the result of corrupted CC data. In an
> NTSC video signal, the CC data is encoded on Line 21 <snip>

>> ... or sometimes just approximations of the phrases used
>> instead of the actual words?

> Sometimes this is done intentionally; sometimes not. An ad libbing
> speaker often speaks in a hesitant manner, sometimes repeating himself
> or inserting extraneous or meaningless words. <snip>

Also, AIU from my reading, there is a rather low limit on the data
rate for line 21, and an even lower limit on the number of lines/words
per second average viewers are assumed able to read. When there is
rapid complex speech it is usually simplified, sometimes sharply, or
less-important prompting or confirmatory lines dropped altogether. And
when there is overlapping speech (or speech with significant
sound/music) pretty often only the "main" speech is captioned.

>> And in the case of VCR or DVD movies, I assume the closed
>> caption is just encoded right on the finished product, is that
>> correct?

VHS definitely, and tapes I record from "air" include it along with
the rest of the video. I don't think DVD actually has the syncs and
(thus) BIs recorded; I believe caption is a separate data stream that
is synthesized into line 21 by the player. I see _very_ low garbles on
DVD play, maybe .01/hour, always corrected on replay and hence likely
faults in my TV (monitor) compared to usually 1-10/hour for
"broadcast" (analog cable) some but far from all of which I find recur
on rebroadcast in cases I can and did check -- presumably this is
either recorded badly on the master or there are data or video
patterns or both especially prone to (self) interference or noise.

Older material like old movies must have captioning added. For
programs created in the last few years, after the FCC mandates for it
became effective, I believe it is mostly done during the final stages
of production. In some cases I see captions that are quite different
from -- and not just shortened forms of -- the spoken lines, which I
suspect were ADRed late but the captioning not changed; and since
caption data must be transmitted a second or two in advance in order
to appear en-bloc in sync with the video, sometimes I see at the end
of a scene a line obviously for a following scene that has been cut.
Conversely this is why a line immediately after a commercial break
usually isn't captioned.

> Yes. It's also true of prerecorded network programming; in fact, it's
> true of just about everything you see on television except live or
> live-delayed programming. <snip examples>

ObSemiTopic: According to my reading much of the realtime captioning
is done by telecommuting. And I have indeed a few times seen Hayesisms
(NO CARRIER, CONNECT nnn) in the captions.

- David.Thompson1 at

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