[Mp4-tech] [video]AVC field selection

[Tourapis, Alexis]

Dear Andrew,
If your macroblock type is in frame mode you can only reference frame pictures. Field pictures can only be referenced by field macroblocks. Can you please clarify? This seems to have nothing to do with having num_ref_idx_l0_active_minus1 set to 0 but with the type of your macroblock. 
Best regards,
Alexis  
-----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 9:40 PM
To: dthoang yahoo.com; mp4-tech lists.mpegif.org
Subject: Re: [Mp4-tech] [video]AVC field selection
Indeed -  in the case I'm considering, the current MB type is frame and it is the case that num_ref_idx_l0_active_minus1 = 0.
That being so, we appear to be agreeing that it is not possible to reference just a single field parity from such an MB.
And what I want to do is just that, unfortunately.
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 9:21 PM
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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