Creates a new, empty extended header instance.
Parse the extended header from data.
The raw extended header bytes.
The ID3v2 major version (3 or 4). Currently the C++ implementation reads the first 4 bytes as a synchsafe integer regardless of version.
ID3v2 extended header (optional, indicated by header flags).
For v2.3: 4-byte big-endian size (excludes itself) + 2-byte flags + padding For v2.4: 4-byte synchsafe size (includes itself) + 1-byte flag count + flags
The C++ TagLib implementation always uses SynchData.toUInt for the size, which also handles buggy software that writes normal big-endian integers.