psshFromMpd
Every PSSH declared for systemId in a DASH MPD, in document order and de-duplicated.
Reads ContentProtection elements whose schemeIdUri matches, taking the init data from a cenc:pssh child, or from an mspr:pro child for PlayReady. Manifests normally repeat the same ContentProtection on every AdaptationSet, so identical boxes are collapsed.
Throws
if the document is not well-formed XML