Code change:
4.8.1. <ins> It is possible to use groups as units of congestion control.  When the sending strategy is understoud, the objects in the group can be assigned sequence numbers and drop priorities that capture the encoding dependencies, such that: an object can only have dependencies with other objects in the same group, an object can only have dependencies with other objects with lower sequence numbers, an object can only have dependencies with other objects with lower or equal drop priorities. This simple rules enable real-time congestion control decisions at relays and other nodes.  The main drawback is that if a packet with a given drop priority is actually dropped, all objects with higher sequence numbers and higher or equal drop priorities in the same group must be dropped.  If the group duration is long, this means that the quality of experience may be lowered for a long time after a brief congestion.  If the group duration is short, this can produce a jarring effect in which the quality of experience drops perdiodically at the tail of the group. 4.8.2. </ins> To enable use cases where receivers may wish to address a particular time of media in addition to having the most recently produced media available, both "pull" and "push" of media SHOULD be supported, with

Related discussion:
text: Section 3.1 For example, rather than waiting for 30 seconds before connecting, the user might quickly download the "key" frames of the past 30 seconds and replay them in order to "synchronize" the video decoder. [BA] I think this sentence points out that the term "access point" may need to be clarified, because in such a scenario, the term "access point" may have a different meaning in stored media than in media transmitted over the wire to speed up join latency. Section 3.2 It is possible to use groups as units of congestion control. When the sending strategy is understoud, the objects in the group can be assigned sequence numbers and drop priorities that capture the encoding dependencies, such that: an object can only have dependencies with other objects in the same group, an object can only have dependencies with other objects with lower sequence numbers, an object can only have dependencies with other objects with lower or equal drop priorities. [BA] This text seems to be mixing distinct concepts such as dependencies and layering. In layered coding, there is typically only a requirement not to depend on higher layers, but it's possible to depend on frames in lower layers. Mixing drop priority (a transport concept) with groups seems confusing to me. The main drawback is that if a packet with a given drop priority is actually dropped, all objects with higher sequence numbers and higher or equal drop priorities in the same group must be dropped. [BA] Leaving gaps in the sequence number space does seem problematic, but that's a choice, not a requirement. If the group duration is long, this means that the quality of experience may be lowered for a long time after a brief congestion. If the group duration is short, this can produce a jarring effect in which the quality of experience drops perdiodically at the tail of the group. [BA] What does "group duration" mean? Are you referring to time between I-frames? This paragraph seems to assume that group duration is a constant rather than something which can be set dynamically. Section 4 Some video codecs have a complex structure. [BA] Are you referring to codecs, or encodings? It would send for example: [BA] A picture might help here.