[Mp4-tech] [video]AVC field selection

[Gary Sullivan]

I don't think there is any ambiguity about it.  Just because the syntax element called mb_field_decoding_flag is not used when field_pic_flag is equal to 1 does not mean that there are no field macroblocks in such a picture.  On the contrary, all macroblocks in such a picture are field macroblocks.
So when I said "field MBs when field_pic_flag is equal to 1", I could have equivalantly just said "when field_pic_flag is equal to 1" with no mention of field MBs, since that aspect is inherent when field_pic_flag is equal to 1.  The only reason I explicitly referred to these being field MBs is to contrast with your statement saying "the inference of ref_idx_l0 only occurs for frame MBs when num_ref_idx_active_minus1 is equal to 0", which did not seem to include the possibility of any field MBs having such inference.
Best Regards,
Gary Sullivan 
+> -----Original Message-----
+> From: Dzung Hoang [mailto:dthoang yahoo.com] 
+> Sent: Wednesday, June 20, 2023 11:50 PM
+> To: Gary Sullivan; 'Andrew Palfreyman (cisco)'; 
+> mp4-tech lists.mpegif.org
+> Subject: RE: [Mp4-tech] [video]AVC field selection
+> 
+> Gary,
+> 
+> This is where the spec has some ambiguity. In 7.3.4, 
+> mb_field_decoding_flag
+> is only present when MbaffFrameFlag is set. However, in 
+> 7.4.4, the semantics
+> of mb_field_decoding_flag only talks about macroblock pairs. 
+> There is no
+> derivation of mb_field_decoding_flag given when 
+> MbaffFrameFlag is not set.
+> 
+> I was assuming that mb_field_decoding_flag is true for field 
+> pictures.
+> 
+> Regards,
+> - Dzung Hoang
+> 
+> 
+> -----Original Message-----
+> From: Gary Sullivan [mailto:garysull windows.microsoft.com] 
+> Sent: Thursday, June 21, 2023 1:31 AM
+> 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
+> +> 
+> +> No virus found in this incoming message.
+> +> Checked by AVG Free Edition. 
+> +> Version: 7.5.472 / Virus Database: 269.9.1/854 - Release 
+> +> Date: 6/19/2007
+> +> 1:12 PM
+> +>  
+> +> 
+> +> No virus found in this outgoing message.
+> +> Checked by AVG Free Edition. 
+> +> Version: 7.5.472 / Virus Database: 269.9.1/854 - Release 
+> +> Date: 6/19/2007
+> +> 1:12 PM
+> +>  
+> +> 
+> +> _______________________________________________
+> +> NOTE: Please use clear subject lines for your posts. Include 
+> +> [audio, [video], [systems], [general] or another 
+> +> apppropriate identifier to indicate the type of question you have.
+> +> 
+> +> Note: Conduct on the mailing list is subject to the 
+> +> Antitrust guidelines found at 
+> +> http://www.mpegif.org/public/documents/vault/mp-out-30042-Ant
+> +> itrust.php
+> +> 
+> 
+> No virus found in this incoming message.
+> Checked by AVG Free Edition. 
+> Version: 7.5.472 / Virus Database: 269.9.1/854 - Release 
+> Date: 6/19/2007
+> 1:12 PM
+>  
+> 
+> No virus found in this outgoing message.
+> Checked by AVG Free Edition. 
+> Version: 7.5.472 / Virus Database: 269.9.1/854 - Release 
+> Date: 6/19/2007
+> 1:12 PM
+>  
+> 
+> 
+>