[FFmpeg-trac] #9724(ffmpeg:new): Duplicate character pairs in Closed Captions

[FFmpeg]

#9724: Duplicate character pairs in  Closed Captions
-------------------------------------+-------------------------------------
             Reporter:  Selcuk       |                     Type:  defect
  Ozturk                             |
               Status:  new          |                 Priority:  normal
            Component:  ffmpeg       |                  Version:  4.4.1
             Keywords:  eia_608,     |               Blocked By:
  closed captions                    |
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------
 Summary of the bug:
 Bug in the handling of eia-608 closed captions. Captions have duplicated
 character pairs. The bug did not exist in ffmpeg versions 4.3.2 and
 earlier.

 How to reproduce:
 You will need a HDHomerun Prime and a cable service with cable card like
 Verizon FIOS or Comcast.
 {{{
 % ffmpeg -i http://192.168.78.45:5004/auto/v103 -c:v libx264 -preset:v
 ultrafast -g 29 -crf 40 -s 128x72 -bsf:v h264_mp4toannexb -map 0:v -f
 mpegts -t 60 z-4.4.1.ts
 % ffmpeg -f lavfi -i movie=z-4.4.1.ts[out+subcc] z-4.4.1.srt
 }}}
 The resulting z-4.4.1.srt file has text like the following:

 ----
 5
 00:00:04,571 --> 00:00:10,410
 <font face="Monospace">{\an7}ABABORORTITIONON,, T THAHATT I I
 TETEXAXASS D DOEOESS H HAVAVEE E</font>

 6
 00:00:10,410 --> 00:00:11,845
 <font face="Monospace">{\an7}TETEXAXASS D DOEOESS H HAVAVEE E
 LALAWSWS T THAHATT A ARERE P PUT</font>
 ----

 Using the old releases available on https://johnvansickle.com/ffmpeg/
 site, I have narrowed down the introduction of the bug somewhere between
 ffmpeg versions 4.3.2 and 4.4.1. All versions up to and including 4.3.2
 are working properly and producing correct closed captions. All versions
 from 4.4.1 on have this bug.

 The problem is at the recording of the TS file and not at the extraction
 of SRT file. Playing the resulting TS file in VLC demonstrates the problem
 in closed captions.

 I can provide both the recorded TS files and the SRT files if needed.
-- 
Ticket URL: <https://trac.ffmpeg.org/ticket/9724>
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