MKVToolNix 61.0.0 (64-bit)

What's new in this version:

New features and enhancements:
- all: IETF BCP 47/RFC 5646 language tags: implemented support for officially registered IANA language tag extensions
- mkvmerge: track selection: when using language tags for selecting which tracks to keep, mkvmerge will now use component-based language tag matching instead of comparing them verbatim. This means that only those components (language, region etc.) the user specified will be required to exist and be equal. For example, if a file contains three subtitle tracks with languages `es` (generic Spanish), `es-MX` (Spanish as spoken in Mexico) and `es-ES` (Spanish as spoken in Spain), the user can use `--stracks es` to match all three tracks or be more specific with e.g. `--stracks es-MX` which would only match one track. Similarly inverting the selection with e.g. `--stracks !es` would get rid of all three tracks, not just the one for the generic Spanish.
- MKVToolNix GUI: multiplexer: deriving track languages from file names: the GUI can now detect full BCP 47/RFC 5646 language tags in file names.
- MKVToolNix GUI: multiplexer: deriving track languages from file names: the default list of boundary characters now includes `-`
- MKVToolNix GUI: multiplexer: the GUI now defaults to the "lower" process priority setting for new installations in order to leave more room for other applications, especially interactive ones. Up to and including v59 the default was the "normal" process priority. v60 changed that to "lowest", which turned out to be much slower on Windows for no real gain over "lower". The setting will be auto-corrected by the GUI if the settings file were saved last with a version between v60.0.0.0 & v60.0.0.17 & "lowest" & it is still set to "lowest".
- HEVC dumper development tool: the tool has been renamed to `xvc_dump` and extended to be able to dump AVC/H.264 bitstreams, too. It now also detects the type of bitstream framing (ISO 14496-15 vs. ITU-T H.264/H.265 Annex B).

Bug fixes:
- all: IETF BCP 47/RFC 5646 language tags: fixed a corner case of wrongfully allowing scripts/variants not listed in any of the entries in the prefix list when the prefix list contains prefixes restricting scripts/variants and a prefix solely with the language at the same time (example: the variant `ekavsk` with its prefixes `sr`, `sr-Cyrl` and `sr-Latn` where e.g. `sr-ekavsk` and `sr-Cyrl-ekavsk` should be allowed but not `sr-Bali-ekavsk`).
- mkvmerge: HEVC/H.265: the frame type of B frames was often wrongfully signalled as P frames instead, both with `BlockGroup` (missing second references) and `SimpleBlock` ("discardable" flag not set) elements.
- mkvmerge: SSA/ASS packetizer: the frame numbers will now be re-calculated when appending SSA/ASS tracks so that frame numbers of appended tracks are always strictly higher than frame numbers of the track they're appended to.
- mkvmerge, MKVToolNix GUI's chapter editor: BCP 47/RFC 5646 language tags: when BCP 47 language tags are used with a language code that isn't part of ISO 639-2, the programs will now write a legacy language element set to `und` ("undetermined") instead of not writing such an element at all or writing one with an invalid code.
- mkvmerge, MKVToolNix GUI's chapter editor: BCP 47/RFC 5646 language tags: the programs will ensure that the legacy and IETF language elements written will be unique within the scope of the same "chapter display" element.
- mkvinfo, MKVToolNix GUI's info tool: in summary mode the frame type was reported wrong for `BlockGroup` elements in which the `ReferenceBlock` elements were located behind the `Block` element.

Build system changes:
- all: `std::codecvt_utf8` is now used instead of Boost's `utf8_codecvt_facet`. The bundled copy the latter in `lib/boost` has therefore been removedMove downloads up and down in the list
- "Save as..." button in Create Download dialog
- BitTorrent settings tab added
- Reset settings to defaults button added
- Remember chosen quality, file type, etc. when creating a new download
- Check for a new version of FDM: show changelog
- "Restore hidden state when finished adding new downloads" option
- "Download link likely expired" dialog
- "Missing Files" filter
- Minor interface improvements
- macOS: full screen mode support
- Android: open download links in the built-in web browser
- Fixed: FDM could not notice file removal in some cases
- Fixed: several days were missing in scheduler's interface
- Fixed: various bugs and problems of exporting/importing downloads
- Fixed: minor interface bugs
- Fixed: Windows: FDM was conflicting with itself when running under different accounts simulteneously
- Fixed: macOS: import data from FDM5 was completely broken
- Fixed: macOS: FDM was using discrete graphics only on macOS supporting switchable devices
- Fixed: Android: magnet links were not intercepted in the built-in browser
- Fixed: Android: in some cases interface was ignoring option to automatically remove downloads with deleted files
- Fixed: Android: built-in web browser was not sending HTTP referrer header in some cases