[FFmpeg-trac] #7843(undetermined:closed): FFmpeg not outputting to spec MKV files

FFmpeg trac at avcodec.org
Tue Apr 16 02:51:17 EEST 2019


#7843: FFmpeg not outputting to spec MKV files
-------------------------------------+-------------------------------------
             Reporter:               |                    Owner:
  alexrichmond                       |
                 Type:  defect       |                   Status:  closed
             Priority:  normal       |                Component:
                                     |  undetermined
              Version:  unspecified  |               Resolution:  duplicate
             Keywords:               |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------
Changes (by mkver):

 * status:  new => closed
 * resolution:   => duplicate


Comment:

 1. As cehoyos has already said, this is not a valid ticket in the current
 form.
 2. Are you sure your subtitles are plain text and that you are not
 accidentally muxing a DVB subtitles stream? Because actually c:s copy
 would AFAIK not work if your input were a teletext stream.
 3. I think I already know what this is about:
 a) FFmpeg writes unknown-length subtitle blocks as BlockGroups with a
 duration element indicating a duration of zero. This is insane and I
 intend to change this (after my current open patchset for the Matroska
 muxer has been dealt with...), but it is not spec-incompliant.
 b) mkvalidator's error is based upon an insane and now removed part of the
 Matroska specs: That a BlockGroup with a duration of zero can't be a
 keyframe. This has since been removed (see https://github.com/Matroska-Org
 /matroska-specification/commit/9313a00f7391a285f95e9d6f0a5f8f3f80ed4779),
 but mkvalidator 0.5.2 has not been fixed. A PR for this is here:
 https://github.com/Matroska-Org/foundation-source/pull/40, but it hasn't
 been accepted yet.
 4. Did you really use a current version of mkvmerge? Newer versions (since
 31.0) keep a BlockGroup with an explicit duration of 0ms that way, so that
 mkvalidator's error should also be emitted for the remuxed file; earlier
 versions mostly muxed such subtitles as SimpleBlocks. The relevant
 mkvmerge issue is 2490: https://gitlab.com/mbunkus/mkvtoolnix/issues/2490
 5. Btw: This is also a duplicate of #2023. Therefore closed.

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Ticket URL: <https://trac.ffmpeg.org/ticket/7843#comment:2>
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