MKVToolNix (64-bit)

What's new in this version:

New features and enhancements:
- mkvmerge, mkvpropedit: tags: the programs will no longer write tag elements that are mandatory and set to their default value (e.g. "tag language" set to `und` = undetermined)
- mkvmerge, mkvpropedit, MKVToolNix GUI chapter editor: chapters: the programs will no longer write chapter elements that are mandatory and set to their default value (e.g. "chapter language" set to `eng` = English or "Chapter flag enabled" = 1)
- mkvextract: chapters: mkvextract will no longer add a `ChapterLanguage` element set to `eng` to the generated XML content if the source file doesn't contain such an element
- MKVToolNix GUI: multiplexer: when using the "tab widget below the files & tracks" layout option for the track properties the elements in the "general options" tab will use six rows à four columns instead of twelve rows à two columns, greatly reducing the required height.

Fixed:
- mkvmerge: AAC reader: fixed mkvmerge aborting to read AAC files bigger than 2 GB with a message about not being able to allocate memory.
- mkvmerge: chapters: `ChapLanguageIETF` elements were still created when the option `--disable-language-ietf` was given after an option leading to the creation of chapters. Now the position doesn't matter anymore.
- mkvmerge: chapters: when the option `--disable-language-ietf` is used ChapLanguageIETF` elements won't be written even when sources are read Matroska files or XML chapters files) that do contain those elements.
- mkvmerge: tags: when the option `--disable-language-ietf` is used TagLanguageIETF` elements won't be written.
- mkvmerge: tags: mkvmerge will no longer write language elements for the track statistics tags it creates, making the effective language "undetermined" due to `und` being the default value for the legacy tag language element.
- mkvmerge: tags: the XML tag parser will now validate all `<Simple>` children of `<Tag>` elements, not just the first for each `<Tag>`
- mkvmerge: tags: the XML tag parser now uses the spec-compliant `und` "undetermined") as the default language for `<Simple>` tags instead of eng`.
- mkvmerge, mkvpropedit: tags: mkvmerge will no longer set the "target type" for track statistics tags (earlier it used `MOVIE`). The "target type value" will still be set to `50`.
- mkvmerge, mkvextract: HEVC/H.265: both programs will now normalize the placement of VPS, SPS and PPS NALUs. Each key frame is prefixed with exactly one copy of the currently active parameter sets. This fixes certain classes of bugs related to splitting/appending.
- mkvinfo: when compiled with newer versions of the `fmt` library, certain numbers were not output correctly (e.g. a track's audio sampling frequency of 48000 might be output as 48)
- MKVToolNix GUI: multiplexer: deriving the track language from the file name will match languages case insensitively again (like versions prior to v55).
- MKVToolNix GUI: multiplexer: under certain circumstances keyboard shortcuts such as `Ctrl+W` for closing the active tab or `Ctrl+R` for starting to multiplex ceased to work until the user did certain other things (such as switching to a different tool & back to the multiplexer or opening the multiplexer menu). This started with v54.
- MKVToolNix GUI: chapter editor: the editor will no longer create empty ChapterCountry` elements when adding a chapter name with no default country selected in the preferences.