[Mp4-tech] [H.264]Question about num_ref_idx_lx_active_minus1

[Marco.Miehe sci-worx.com]

Dear Members
I post this mail again. Please can someone clarify this.  
-----Original Message-----
From: mp4-tech-bounces lists.mpegif.org
[mailto:mp4-tech-bounces lists.mpegif.org] On Behalf Of Miehe Marco
(SCI)
Sent: Friday, April 28, 2024 4:01 PM
To: Mp4-tech lists.mpegif.org
Subject: RE: [Mp4-tech] [H.264]Question about
num_ref_idx_lx_active_minus1
I agree with you, but that's not the point.
Let's consider the case that MbaffFrameFlag = 1, i.e., as you say,
mb_adaptive_frame_field_flag = 1 and field_pic_flag = 0. 
This means, we have an Mbaff Frame. Now, for a field macroblock, the
semantics of num_ref_idx_lx_active_minus1 
in the slice header say that the maximum index value is
2*num_ref_idx_lx_active_minus1 + 1, and that the range of
num_ref_idx_lx_active_minus1 is from 0 to 15. This results in a maximum
possible index value of 2*15 + 1 = 31, 
which is logical since there can be up to 32 reference fields in the
reference list for a field MB.
But in the semantics of the same syntax element in the Picture Parameter
Set, it again says that for field MBs in Mbaff 
frames the maximum index value is 2*num_ref_idx_lx_active_minus1 + 1,
but the range of num_ref_idx_lx_active_minus1 
here is only limited from 0..31. This now looks as if the maximum
possible reference index is 2*31 + 1 = 63, 
which does not makes sense regarding the maximum number of 32 reference
fields.
I believe that the semantics should be the same as for
num_ref_idx_lx_active_minus1 in the slice header and 
everything would be clear. I think this is just an inaccurate
description here which should be corrected.
BR,
Marco Miehe
-----Original Message-----
From: mp4-tech-bounces lists.mpegif.org
[mailto:mp4-tech-bounces lists.mpegif.org] On Behalf Of
Ye-Kui.Wang nokia.com
Sent: Wednesday, April 26, 2024 1:18 PM
To: Mp4-tech lists.mpegif.org
Subject: RE: [Mp4-tech] [H.264]Question about
num_ref_idx_lx_active_minus1
Note that MbaffFrameFlag = ( mb_adaptive_frame_field_flag  &&
!field_pic_flag ), i.e. when field_pic_flag == 1, MbaffFrameFlag = 0.  
BR, YK
-----Original Message-----
From: mp4-tech-bounces lists.mpegif.org 
[mailto:mp4-tech-bounces lists.mpegif.org]
Sent: 25 April, 2006 15:23
To: Mp4-tech lists.mpegif.org
Subject: [Mp4-tech] [H.264]Question about num_ref_idx_lx_active_minus1
Dear Members
I have a question regarding the max size of the reference picture list.
In the standard ITU-T Rec. H.264 chapter 7.4.3 (Slice header semantics)
the variable 
"num_ref_idx_lx_active_minus1" says if the field_pic_flag is equal to 0
the max. size 
of the ref. pic. list is 16. And otherwise (field_pic_flag is equal to
1) the max. size
of the ref. pic. list is 32 (num_ref_idx_lx_active_minus1 shall be in
range of 0..31).
The variable "num_ref_idx_lx_active_minus1" is also in the
PictureParameterSet.
I think this definition could be misunderstood. 
Picture parameter set semantics (chapter 7.4.2.2):
... When MbaffFrameFlag is equal to 1, num_ref_idx_l0_active_minus1 is
the maximum index value for the 
decoding of frame macroblocks and 2 * num_ref_idx_l0_active_minus1 + 1
is the maximum index value for the 
decoding of field macroblocks. The value of num_ref_idx_l0_active_minus1
shall be in the range of 0 to 31, 
inclusive.
When I read this definition I might think (altough I think it dosen't
make sense) 
the max. size of the ref. pic list is 64.
Up to now I thought the Max. Size of the DPB is 16 and the max. size of
the reference picture list is also
16 or 32 (in case of fields).
I'd appreciate if some one clarifies this.
Best regards,
Marco Miehe
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[video], [systems], [general] or another apppropriate identifier to
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Note: Conduct on the mailing list is subject to the Antitrust guidelines
found at
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