[FFmpeg-trac] #11591(avcodec:new): closed captions side data gets corrupted by mpeg2 encoder

[FFmpeg]

#11591: closed captions side data gets corrupted by mpeg2 encoder
-------------------------------------+-------------------------------------
             Reporter:  Jacob        |                     Type:  defect
  Lifshay                            |
               Status:  new          |                 Priority:  normal
            Component:  avcodec      |                  Version:  git-
                                     |  master
             Keywords:               |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------
 Summary of the bug:
 I discovered that closed captions side data gets corrupted by the mpeg2
 encoder, I was able to bisect it to:
 6e225123d8583f avcodec/mpeg12enc: Simplify writing bits
 https://git.ffmpeg.org/gitweb/ffmpeg.git/commitdiff/6e225123d8583f

 How to reproduce:
 Download the Closedcaption_rollup.m2v file from ffmpeg's rsync server to
 ~/Downloads/Closedcaption_rollup.m2v
 Install ffmpeg 7:5.1.6-0+deb12u1 from Debian 12
 {{{
 ./configure --assert-level=2 --disable-vulkan --disable-stripping
 --optflags=-Og
 make -j$(nproc)
 ffmpeg -y -i ~/Downloads/Closedcaption_rollup.m2v cc_rollup-good.mxf
 ./ffmpeg -y -i ~/Downloads/Closedcaption_rollup.m2v cc_rollup-test.mxf
 ./ffmpeg -y -f lavfi -i "movie=cc_rollup-good.mxf[out+subcc]" -map 0:s
 -c:s copy -f rcwt cc_rollup-good.mxf.rcwt
 ./ffmpeg -y -f lavfi -i "movie=cc_rollup-test.mxf[out+subcc]" -map 0:s
 -c:s copy -f rcwt cc_rollup-test.mxf.rcwt
 diff -y <(hexdump -C cc_rollup-good.mxf.rcwt) <(hexdump -C cc_rollup-
 test.mxf.rcwt)
 }}}

 the first closed caption chunk on the good one is just:
 {{{
 fc 80 80  fd 80 80
 }}}
 but on the bad commit it is:
 {{{
 fc 80 80  fd 80 80  0f f0 00  23 f8 75  94 88 b2
 d4 68 52  e3 45 a1  8b 2d 46  85 22 2c  b5 1a 14
 d4 85 22  2c d1 a1  8b 2d 06  a5 22 2c  b5 1a 14
 d4 68 47
 }}}

 that is far from the only one that's bad.
-- 
Ticket URL: <https://trac.ffmpeg.org/ticket/11591>
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