The CDP Interface carries the CEA-708/SMPTE 334-2 Caption Distribution Packet (CDP). This is principally intended for use in cases where there is a desire to provide some or all of the following information for downstream use: caption data; caption service descriptors; and time codes. In one typical application, a DTVCC caption server could use this interface to send CDPs to a 334M VANC encoder.
SMPTE 333M specifies an interface that is widely used for providing caption data and service information to ATSC emission encoders. The older Grand Alliance interface can also be used for this same purpose. It is included here as Annex B to document its use in this application.