ST2110SenderSender.SubtitleSender

ST 2110-40 subtitle sender. Wire-identical to AncillarySender — same SMPTE 291 / RFC 8331 framing, same SDP — but accepts Subtitle stream inputs (CEA-708 / CEA-608 / OP-47) instead of Ancillary stream inputs. Discriminated at the PS sender layer so the Outputs/ST2110 pin generators can be narrowly typed. A wire stream that needs to carry both subtitles AND ancillary today takes two separate senders (one of each).