[FFmpeg-trac] #3623(undetermined:reopened): Mixed results writing M4A metadata

[FFmpeg]

#3623: Mixed results writing M4A metadata
-------------------------------------+-------------------------------------
             Reporter:  svnpenn      |                    Owner:
                 Type:  defect       |                   Status:  reopened
             Priority:  normal       |                Component:
                                     |  undetermined
              Version:  git-master   |               Resolution:
             Keywords:  mov          |               Blocked By:
  metadata                           |
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------

Comment (by svnpenn):

 Based on Tom's answer, I think I was able to solve this. If I run these
 commands:

 {{{
 ffmpeg -i in.m4a -c copy -movflags faststart -metadata title=Confetti
 bad.m4a
 ffmpeg -i in.m4a -c copy -movflags faststart -metadata title=Confetti `
    -map_metadata -1 good.m4a
 mp4dump bad.m4a > bad.txt
 mp4dump good.m4a > good.txt
 git diff bad.txt good.txt
 }}}

 I get this result:

 {{{
 -        handler_name = ISO Media file produced by Google Inc.
 +        handler_name = SoundHandler
 }}}

 I tested some more, and it seems any `handler_name` more than **29
 characters** will fail, which is probably 30 including a null byte, or
 maybe a length byte. Here is an example that will just barely pass:

 {{{
 ffmpeg -i in.m4a -c copy -movflags faststart -metadata title=Confetti `
 -metadata:s handler_name=SoundHandlerSoundHandlerSound good.m4a
 }}}

--
Ticket URL: <https://trac.ffmpeg.org/ticket/3623#comment:17>
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