12.2. Video Telephony, No Slice Data Partitioning, No NAL Unit Aggregation

12.2. Video Telephony, No Slice Data Partitioning, No NAL Unit Aggregation

The RTP part of this scheme is implemented and tested (though not the control-protocol part; see below).

In most real-world video telephony applications, picture parameters such as picture size or optional modes never change during the lifetime of a connection. Therefore, all necessary parameter sets (usually only one) are sent as a side effect of the capability exchange/announcement process, e.g., according to the Session Description Protocol (SDP) syntax specified in Section 8.2 of this document. As all necessary parameter set information is established before the RTP session starts, there is no need for sending any parameter set NAL units. Slice data partitioning is not used either. Thus, the RTP packet stream basically consists of NAL units that carry single coded slices.

The encoder chooses the size of coded slice NAL units so that they offer the best performance. Often, this is done by adapting the coded slice size to the maximum transmission unit (MTU) size of the IP network. For small picture sizes, this may result in a one-picture-per-one-packet strategy. Intra refresh algorithms clean up the loss of packets and the resulting drift-related artifacts.