JCTVC-B031 [K. Kazui, J.Koyama, A.Nakagawa (Fujitsu)] Proposal of requirement on very low delay coding
Low delay less than 100 ms. In CBR applications, usage of I refresh picture (due to buffering) would violate this constrained. Approach: "Intra MB line refresh" (horizontal or vertical, only part of picture is refreshed). Reference to non-refreshed area should be prohibited (encoder issue). It is however necessary to have a new slice boundary at the boundary of the refreshed MB row (in order to guarantee decodability). Such a scheme introduces overhead, i.e. loses quality. This is in particular true for the vertical scheme.
Proposal to introduce information about position of refreshed area in the slice/picture header. "Asymmetric limitation of reference" disallows references from a refreshed area to a non-refreshed area. Also, de-blocking filtering using samples from non-refreshed areas must be disallowed, and motion compensation taking reference from non-refreshed areas shall be disallowed, therefore it is suggested to define extension/extrapolation from refreshed into non-refreshed areas of reference pictures.
No results were shown to illustrate that the suggested method really provides a benefit in terms of compression.
It is not high priority currently to include specialized measures like this in the TMuC design. Current TMuC software does not support multiple slices per picture yet.
Constrained intra prediction also should in principle provide similar functionality.
Further study was recommended, more results would need to be presented.
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