TtmlCaps interface

Capabilities for an ST 2110-43 TTML receiver. media_types is effectively pinned to application/ttml+xml. acceptedCodecs is the list of IMSC profile short codes ("im1t", "im2t", etc.) the receiver will decode — controllers can use the matching IS-04 cap to pair only with senders advertising compatible profiles. Empty list = accept any codecs= value.

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