Log Message:
mkvtoolnix: updated to 21.0.0

Version 21.0.0 "Tardigrades Will Inherit The Earth"

New features and enhancements
* mkvmerge: track statistics tags: the TagDefault element will not be
  written anymore as it was always set to the default value 1
  anyway. Implements 2202.
* mkvmerge, MKVToolNix GUI: JSON files can now contain C++-style line comments
  outside of strings (e.g. something like this: // this is ignored). Such
  comments, even though not part of the official JSON specifications, are now
  ignored when reading JSON files.
* MKVToolNix GUI: chapter editor: opening a Matroska file without chapters in
  it will now open the file in an empty chapter editor instead of showing an
  error message. Implements 2218.
* MKVToolNix GUI: an "info" tool has been added, replacing the \ 
functionality
  of mkvinfo's GUI. The functionality is not on par yet but will be for
  release v22. Implements most of the functionality of 2104.

Bug fixes
* build system: configure was treating --disable-ubsan and
  --disable-addrsan the same as --enable-ubsan and
  --enable-addrsan.
* build system: an error message is output if a command to execute is not
  found instead of silently failing.
* build system: in addition to looking for the gettext C function and
  library, configure now also verifies the presence of the msgfmt program
  instead of simply relying on it.
* mkvmerge: appending files with additional parts at the same time was broken
  if more than one additional part was appended (e.g. when appending files
  from DVDs with something like '(' VTS_01_1.VOB VTS_01_2.VOB ')' + '('
  VTS_02_1.VOB VTS_02_2.VOB ')'). In such a situation the content from files
  VTS_02_1.VOB and VTS_02_2.VOB where laid out in parallel to the content
  from the earlier files.
* mkvmerge: FLV reader: a single invalid AAC frame was written for AAC audio
  tracks with codec initialization data longer than five bytes.
* mkvmerge: FLV reader: timestamps will be normalized down to 0.
* mkvmerge: MP4 reader: if an AAC track doesn't contain an AAC-specific
  decoder configuration in the ESDS portion, then a default decoder
  configuration will be generated based on the track's header data instead of
  skipping the track.
* mkvmerge: MP4 reader: fixed reading HEVC/h.265 video tracks if they're
  stored as Annex B byte streams inside MP4.
* mkvmerge: Ogg Opus reader: mkvmerge will now emit a warning instead of
  aborting when it encounters an Ogg Opus page with no data in the
  packet.
* mkvmerge, mkvextract: Matroska parser: fixed a segmentation fault that
  occurred whenever the first level 1 element after resyncing after an error
  in the file structure isn't a cluster.
* mkvmerge, MKVToolNix GUI multiplexer & header editor: fixed a crash during
  --enable-addrsan.
* build system: an error message is output if a command to execute is not
* build system: an error message is output if a command to execute is not
  found instead of silently failing.
* build system: in addition to looking for the gettext C function and
  library, configure now also verifies the presence of the msgfmt program
  instead of simply relying on it.
* mkvmerge: appending files with additional parts at the same time was broken
  if more than one additional part was appended (e.g. when appending files
  from DVDs with something like '(' VTS_01_1.VOB VTS_01_2.VOB ')' + '('
  VTS_02_1.VOB VTS_02_2.VOB ')'). In such a situation the content from files
  VTS_02_1.VOB and VTS_02_2.VOB where laid out in parallel to the content
  from the earlier files.
* mkvmerge: FLV reader: a single invalid AAC frame was written for AAC audio
  tracks with codec initialization data longer than five bytes.
* mkvmerge: FLV reader: timestamps will be normalized down to 0.
* mkvmerge: MP4 reader: if an AAC track doesn't contain an AAC-specific
  decoder configuration in the ESDS portion, then a default decoder
  configuration will be generated based on the track's header data instead of
  skipping the track.
* mkvmerge: MP4 reader: fixed reading HEVC/h.265 video tracks if they're
  stored as Annex B byte streams inside MP4.
* mkvmerge: Ogg Opus reader: mkvmerge will now emit a warning instead of
  aborting when it encounters an Ogg Opus page with no data in the
  packet.
* mkvmerge, mkvextract: Matroska parser: fixed a segmentation fault that
  occurred whenever the first level 1 element after resyncing after an error
  in the file structure isn't a cluster.
* mkvmerge, MKVToolNix GUI multiplexer & header editor: fixed a crash during
  file type detection for attachments if MKVToolNix is installed in a path
  with non-ASCII characters (e.g. German Umlauts).
* mkvinfo: the --hex-positions parameter did nothing in summary mode.
* mkvinfo: Windows: line endings will be written as \r\n (carriage return &
  line feed) again instead of just \n (line feed).
* mkvpropedit: adding track statistics tags: for tracks with content encoding
  (compression) mkvpropedit is now accounting the uncompressed number of
  bytes, not the encoded (compressed) number of bytes.
* MKVToolNix GUI: multiplexer: the subtitle character set can now be set for
  appended subtitle files, too.
* MKVToolNix GUI: multiplexer: when appending, all tracks appended to disabled
  tracks will start out disabled, too.

Build system changes
* mkvinfo: the GUI portion has been removed. mkvinfo is now a pure
  command-line program again.