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.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.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.It now also detects the type of bitstream framing (ISO 14496-15 vs. HEVC dumper development tool: the tool has been renamed to 'xvc_dump' and extended to be able to dump AVC/H.264 bitstreams, too.MKVToolNix GUI: multiplexer: deriving track languages from file names: the GUI can now detect full BCP 47/RFC 5646 language tags in file names and the default list of boundary characters now includes '-'.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.IETF BCP 47/RFC 5646 language tags: implemented support for officially registered IANA language tag extensions.

Mp4 toolnix