MKVToolNix 50.0.0 (64-bit)

What's new in this version:

New:
- mkvmerge: IETF BCP 47/RFC 5646 language tags: mkvmerge will now accept full BCP 47 language tags for all options taking a language. mkvmerge will always write "LanguageIETF" track header elements. If the language tag contains a valid ISO 639-2 language code it will also set the legacy "Language" track header element to the included ISO 639-2 code. Part of the implementation of#2419.
- mkvmerge: IETF BCP 47/RFC 5646 language tags: if present the "LanguageIETF" track header element will be reported as the`language_ietf` property in JSON identification mode. Part of the implementation of #2419.
- mkvmerge: IETF BCP 47/RFC 5646 language tags in chapters: mkvmerge will now write "ChapLanguageIETF" elements when creating chapter atoms, either when reading the simple chapter format or when generating chapters due to the `--generate-chapters` command line option. Part of the implementation of #2419.
- mkvmerge: IETF BCP 47/RFC 5646 language tags in tags: mkvmerge will now write "TagLanguageIETF" elements when creating "simple tag" elements, either when reading tag XML files or when generating them. Part of the implementation of #2419.
- mkvmerge: IETF BCP 47/RFC 5646 language tags: added an option `--disable-language-ietf` that causes mkvmerge to only write the legacy language elements.
- mkvmerge, mkvpropedit, MKVToolNix GUI's chapter editor: IETF BCP 47/RFC 5646 language tags in chapters: when reading XML chapter files the programs will now add "ChapLanguageIETF" elements for atoms that don't contain them. The values are derived from existing "ChapterLanguage" elements. Part of the implementation of #2419.
- mkvpropedit: IETF BCP 47/RFC 5646 language tags: setting/deleting the track language now acts on both the old language element as well as the "LanguageIETF" track header element. Part of the implementation of #2419.
- mkvpropedit: IETF BCP 47/RFC 5646 language tags: added an option`--disable-language-ietf` that causes mkvpropedit to apply changes to the`language` track header property only to the legacy language track header element.
- mkvinfo: IETF BCP 47/RFC 5646 language tags: added support for the "LanguageIETF" track header element. Part of the implementation of #2419.
- MKVToolNix GUI: multiplexer: added full support for IETF BCP 47/RFC 5646 language tags for both track and chapter languages. Part of the implementation of #2419.
- MKVToolNix GUI: chapter: added full support for IETF BCP 47/RFC 5646 language tags for chapter languages. Part of the implementation of #2419.
- MKVToolNix GUI: header editor: added full support for IETF BCP 47/RFC 5646 language tags for track header languages. The header editor allows editing of the legacy language elements and the IETF BCP 47 language elements independent of each other. Part of the implementation of #2419.

Other new features and enhancements:
- mkvmerge: the chapter generation mode `when-appending` now also works with the splitting modes `parts:` & `parts-frames:` when using the `…,+…` syntax for appending other sections of the source file to the same destination file. Implements #2898.
- MKVToolNix GUI: multiplexer: the file selection dialogs now include the extension `.dtsma` for DTS files. Implements #2901.
- mkvmerge: MP4 reader: sped up parsing MP4 DASH files with a lot of segments (`trun` atoms) quite a bit. Part of the fix of #2900.
- The PCRE2 regular expression library is now used instead of `std::regex` for big performance improvements in all places where regular expressions are used for parsing big chunks of text, e.g. in the subtitle parsers. Part of the fix of #2899.
- all programs: Windows: all programs now support long file names on Windows 10 release 1604 if they're turned on in the registry. Implements #2916.

Bug fixes:
- MKVToolNix GUI: preferences: under certain conditions changing the selected entry in the page tree on the left did not cause the page shown on the right to be updated. Fixes #2895.
- mkvmerge: splitting text by a fixed string (e.g. `,`) is now done by using `std::string.find()` instead of using a regular-expression-based text splitting function, greatly improving its performance. Part of the fix of #2899.
- mkvmerge: mkvmerge will now read-buffer file I/O when probing text file formats which increases its speed significantly on Windows. Part of the fix of #2899.
- mkvmerge: MP4 reader: fixed handling of `tkhd` atoms of version 1

Build system changes:
- The PCRE2 library (the 8-bit variant) is now required