[Mp4-tech] [H.264]A question about the "initialisation process for reference picture lists for B slices in frames"

[Gary Sullivan]

Tan Rui et al,
I believe I can confirm your understanding.  A key reason that we do not
include the "non-existing" pictures in the lists when the POC type is 0
is that we don't know what their POC values are, so we would not know
where to put them in the list even if we wanted to.
I suggest not looking for too much deep meaning in the initial ordering
of the lists.  The idea is just to set up some basically-reasonable
initial order.  The encoder can change the order if it does not like the
initial ordering, and the syntax to make such changes seems pretty
efficient.
Best Regards,
Gary Sullivan
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	From: mp4-tech-bounces lists.mpegif.org
[mailto:mp4-tech-bounces lists.mpegif.org] On Behalf Of Tan Rui --
Huawei
	Sent: Monday, July 24, 2023 8:10 PM
	To: mp4-tech lists.mpegif.org
	Subject: [Mp4-tech] [H.264]A question about the "initialisation
process for reference picture lists for B slices in frames"
	Hi, all experts,
	When I read the 8.2.4.2.3 section about the ""initialization
process for reference picture lists for B slices in frames",
	I found the following description:
	For B slices, the order of short-term reference entries in the
reference picture lists RefPicList0 and RefPicList1 depends
	on output order, as given by PicOrderCnt( ). When
pic_order_cnt_type is equal to 0, reference pictures that are marked
	as "non-existing" as specified in subclause 8.2.5.2 are not
included in either RefPicList0 or RefPicList1.
	I guess that when pic_order_cnt_type is equal to 0, the POC
information must be extracted from the slice header. If the reference
pictures are
	marked as "non-existing", the decoder can not get the correct
information from them. So that, the protocol said these conditions shall
not be
	included in either RefPicList0 or RefPicList1. Can someone tell
me the true meaning in the protocol? Thanks.
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