Log Message:
mkvtoolnix: updated to 68.0.0

Version 68.0.0 "The Curtain" 2022-05-22

New features and enhancements

* mkvmerge: HDMV PGS subtitles: mkvmerge now tries to detect bogus timestamps
  (where the current timestamp is two hours or more after the previous
  timestamp) & correct them to something more sensible (1s after the previous
  timestamp). That way one bogus timestamp cannot cause the rest of the frames
  to not be interleaved properly with the other audio & video
  packets.
* mkvmerge: added colour information, colour mastering meta information &
  video projection information properties to the JSON identification
  format. The properties are reported for container types for which mkvmerge
  supports reading them (Matroska & MP4). The JSON identification format
  version number has been bumped to v15.
* MKVToolNix GUI: multiplexer: added controls for all the video colour
  information & the video projection information.

Bug fixes

* mkvmerge: SRT reader: entries with a duration of 0 or less will now be
  skipped.
* mkvpropedit, MKVToolNix GUI's chapter & header editors: fixed an invalid
  memory access when trying to update existing Matroska files whose EBML Head
  element had a "size" field length of eight bytes, and where \ 
rewriting said
  element would shrink the element by one byte. Files created by gstreamer fit
  the first part whereas the second depends on the changes requested by the
  user.
* mkvpropedit, MKVToolNix GUI's chapter & header editors: fixed the programs
  not handling having to remove EBML void elements at the end of the file
  correctly and consequently aborting.
* MKVToolNix GUI: the GUI now uses almost all SVG icons, allowing proper
  scaling even for scaling factors such as 125%.
* MKVToolNix GUI: when compiled with Qt 5 the character set of INI files is
  forced to UTF-8 in order to fix reading INI files written by a version
  compiled with Qt 6.

Build system changes

* Qt's SVG library is now required.