Photon is a Java implementation of the Interoperable Master Format (IMF) standard. IMF is a SMPTE standard whose core constraints are defined in the specification st2067-2:2013
The following IMSC 1.1 profile URIs should probably be added to the checks of NamespaceURI item of the Timed Text descriptor (only for IMF 2020 compositions):
http://www.w3.org/ns/ttml/profile/imsc1.1/texthttp://www.w3.org/ns/ttml/profile/imsc1.1/imageurn:ebu:tt:distribution:2014-01http://www.w3.org/ns/ttml/profile/sdp-us
The following IMSC 1.1 profile URIs should probably be added to the checks of
NamespaceURIitem of the Timed Text descriptor (only for IMF 2020 compositions):http://www.w3.org/ns/ttml/profile/imsc1.1/texthttp://www.w3.org/ns/ttml/profile/imsc1.1/imageurn:ebu:tt:distribution:2014-01http://www.w3.org/ns/ttml/profile/sdp-ushttps://github.com/Netflix/photon/blob/3f4677e92be1a4e85bc2f4f3a1df31329d0fbb29/src/main/java/com/netflix/imflibrary/IMFConstraints.java#L52