12.1. Video Telephony According to Annex A of ITU-T Recommendation H.241

12.1. Video Telephony According to Annex A of ITU-T Recommendation H.241

H.323-based video telephony systems that use H.264 as an optional video compression scheme are required to support Annex A of H.241 [3] as a packetization scheme. The packetization mechanism defined in this Annex is technically identical with a small subset of this specification.

When a system operates according to Annex A of H.241, parameter set NAL units are sent in-band. Only single NAL unit packets are used. Many such systems are not sending instantaneous decoder refresh (IDR) pictures regularly, but only when required by user interaction or by control protocol means, e.g., when switching between video channels in a Multipoint Control Unit (MCU) or for error recovery requested by feedback.