[Mp4-tech] [video]AVC field selection

[Gary Sullivan]

No (depending on what you mean by "corresponding field").  It means that the field MB will be predicted from whatever field is in the final reference picture list (when that list contains only one field).  That field could be any reference field that ever preceded the current picture (in decoding order), as long as that field is still in the DPB and is still marked as "used for reference".
Best Regards,
Gary Sullivan
+> -----Original Message-----
+> From: V, Rajesh [mailto:Rajesh.Vijayakumar analog.com] 
+> Sent: Wednesday, June 20, 2023 11:52 PM
+> To: Gary Sullivan; dthoang yahoo.com; Andrew Palfreyman 
+> (cisco); mp4-tech lists.mpegif.org
+> Subject: RE: [Mp4-tech] [video]AVC field selection
+> 
+> So when field_pic_flag == 1 and num_ref_idx_lX_active_minus1 
+> == 0, does
+> this inference mean that the field_mb will predict the fields from
+> corresponding field only ?
+> 
+> -----Original Message-----
+> From: mp4-tech-bounces lists.mpegif.org
+> [mailto:mp4-tech-bounces lists.mpegif.org] On Behalf Of Gary Sullivan
+> Sent: Thursday, June 21, 2023 12:01 PM
+> To: dthoang yahoo.com; Andrew Palfreyman (cisco);
+> mp4-tech lists.mpegif.org
+> Subject: RE: [Mp4-tech] [video]AVC field selection
+> 
+> The inference also occurs for field MBs when field_pic_flag 
+> is equal to
+> 1 and num_ref_idx_lX_active_minus1 == 0.
+> 
+> Best Regards,
+> 
+> Gary
+> 
+> +> -----Original Message-----
+> +> From: mp4-tech-bounces lists.mpegif.org 
+> +> [mailto:mp4-tech-bounces lists.mpegif.org] On Behalf Of 
+> Dzung Hoang
+> +> Sent: Wednesday, June 20, 2023 9:22 PM
+> +> To: 'Andrew Palfreyman (cisco)'; mp4-tech lists.mpegif.org
+> +> Subject: RE: [Mp4-tech] [video]AVC field selection
+> +> 
+> +> According to 7.3.5.1, the inference of ref_idx_l0 only occurs for 
+> +> frame MBs when num_ref_idx_l0_active_minus1 = 0. Is there another 
+> +> case that I'm missing? If not, then no field-based prediction can 
+> +> happen in the case you are concerned with.
+> +> 
+> +> Regards,
+> +> - Dzung Hoang
+> +> 
+> +> -----Original Message-----
+> +> From: Andrew Palfreyman (cisco) [mailto:anpalfre cisco.com]
+> +> Sent: Wednesday, June 20, 2023 10:46 PM
+> +> To: dthoang yahoo.com; mp4-tech lists.mpegif.org
+> +> Subject: Re: [Mp4-tech] [video]AVC field selection
+> +> 
+> +> The problem I have with that approach is that in 7.4.5.1 
+> it states 
+> +> "When only one reference picture is used for inter 
+> prediction, the 
+> +> values of
+> +> 
+> +> ref_idx_l0[mbPartIdx] shall be inferred to be equal to 0".
+> +> So even though the ref. pic has two field parities, these 
+> cannot be 
+> +> differentiated via a zero value of ref_idx.
+> +> 
+> +> Best,
+> +> Andrew
+> +> 
+> +> ----- Original Message -----
+> +> From: "Dzung Hoang" <dthoang yahoo.com>
+> +> To: "'Andrew Palfreyman (cisco)'" <anpalfre cisco.com>; 
+> +> <mp4-tech lists.mpegif.org>
+> +> Sent: Wednesday, June 20, 2023 8:08 PM
+> +> Subject: RE: [Mp4-tech] [video]AVC field selection
+> +> 
+> +> 
+> +> > Try LSB of ref_idx XOR with current field parity.
+> +> >
+> +> > Regards,
+> +> > - Dzung Hoang
+> +> >
+> +> > -----Original Message-----
+> +> > From: mp4-tech-bounces lists.mpegif.org 
+> +> > [mailto:mp4-tech-bounces lists.mpegif.org] On Behalf Of
+> +> Andrew Palfreyman
+> +> > (cisco)
+> +> > Sent: Wednesday, June 20, 2023 12:04 PM
+> +> > To: mp4-tech lists.mpegif.org
+> +> > Subject: [Mp4-tech] [video]AVC field selection
+> +> >
+> +> > For AVC, I am trying to identify (with little success so
+> +> far) the semantic
+> +> > equivalent of what in MPEG2 was called
+> +> motion_vector_field_select. How is
+> +> > this accomplished in AVC?
+> +> >
+> +> > Best,
+> +> > Andrew
+> +> 
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