matrixSpecified

False when the source declared no matrix and matrix is this library's guess.

The guess is right for nearly all video and wrong for the rest, so a consumer that has a better answer (a container-level hint, a user override) can tell which fields it is allowed to overrule and which are the file's own word. Every guess made anywhere is the standard-versus-high-definition rule in guessFor, so a guessed field is never HDR.