matrixSpecified

True when the container or codec DECLARED this matrix, false when guessFor supplied it.

A guessed value is a good default and a bad fact. Tone mapping, a colour-managed compositor and a remux that copies tags all want to know which they are holding: copying a guess into an output declares something the source never said. Range has carried this distinction from the start; these three did not, so every consumer saw BT.709 and could not tell whether the file said so or whether it was 1080 lines tall.