[Mp4-tech] [video]AVC field selection

[Dzung Hoang]

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
+> 
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