[Mp4-tech] Re: Mp4-tech Digest, Vol 56, Issue 9

[pankaj bajpai]

Hi Jay,
I am trying to answer your question.
Request group members to correct me wherever i am wrong.
1) What is the 'decoded VOP area' of a rectangular VOP? Is it the area of
> the so-called 'displayable part' of the VOP (800×600), or is it the full
> coded VOP area (800×608)?

Ans: I am not very clear from your question about decoded area.
Still i'll try to answer. Yes initial decoded area is the coded area, ie area  including padding to satisfy multiplicity with 16. However, all post processing should be done wrt displayable area.
>   2) If the 'decoded VOP area' refers to the full coded VOP area including
> extensions, what would the extended parts contain? Would they contain the
> actual coded information (I assume that there are no requirements to what
> that would be), or should the so-called repetitive padding process of
> section 7.6.1 be applied to the extended parts (although that section begins
> with that the padding process is defined for "...samples outside the VOP for
> prediction of arbitrarily shaped objects")?

ans: The extended portion is always generated using repetitive Padding process. However, for rectangual VOP case, this lead to just extending boundaries , and hence, is same as restricting the motion vectors.
> ----- Original Message -----
> From: mp4-tech-request lists.mpegif.org
> To: mp4-tech lists.mpegif.org
> Subject: Mp4-tech Digest, Vol 56, Issue 9
> Date: Tue, 11 Mar 2024 12:07:13 -0400 (EDT)
> 
> 
> Send Mp4-tech mailing list submissions to
> 	mp4-tech lists.mpegif.org
> 
> To subscribe or unsubscribe via the World Wide Web, visit
> 	http://lists.mpegif.org/mailman/listinfo/mp4-tech
> or, via email, send a message with subject or body 'help' to
> 	mp4-tech-request lists.mpegif.org
> 
> You can reach the person managing the list at
> 	mp4-tech-owner lists.mpegif.org
> 
> When replying, please edit your Subject line so it is more specific
> than "Re: Contents of Mp4-tech digest..."
> 
> Today's Topics:
> 
>     1. [Mp4-tech][video][MPEG4] MV limitation and bounding rectangle
>        of a	rectangular VOP (J. Miles)
> 
> From: J. Miles <video.codec.help gmail.com>
> To: mp4-tech lists.mpegif.org
> Subject: [Mp4-tech][video][MPEG4] MV limitation and bounding rectangle of a rectangular VOP
> Date: Tue, 11 Mar 2024 09:50:53 +0100
> 
> 
> Hi everyone!
> 
> 
> 
> While working with MPEG-4 (Part 2, not AVC) decoding, I have been looking at
> the use of unrestricted motion vectors in relation to the MV limitation to
> bounding rectangles and find that the Standard (sections 7.6.1-7.6.4) is not
> entirely clear on that. Let me try to describe the case:
> 
> 
> 
> The video bitstreams handled are purely coded as usual rectangular objects
> (no sprites or shapes). In the situation, where the video_object_layer_width
> and/or video_object_layer_height are not dividable by 16, the coded size is
> extended so that it is dividable by 16 and fits with complete MBs. For
> instance, a VOL size of 800×600 would have the coded size being 800×608 to
> fit with an integral number of MBs in the height. As motion vectors are
> allowed to be unrestricted, they may point outside the actual VOL area and
> into the extended VOL area and actually also outside that area. This has an
> impact on the MV limitation described in section 7.6.4 for unrestricted
> motion vectors because the MV is limited "...to the last full pel position
> inside the decoded VOP area". In that section and the other related sections
> of the Standard, there are mostly references to arbitrarily shaped objects
> and not that many to rectangular objects. Although in section 7.6.4, the
> bounding rectangle of a rectangular VOP is defined as being equal to the
> coded (and extended) area.
> 
> 
> 
>   1) What is the 'decoded VOP area' of a rectangular VOP? Is it the area of
> the so-called 'displayable part' of the VOP (800×600), or is it the full
> coded VOP area (800×608)?
> 
> 
> 
>   2) If the 'decoded VOP area' refers to the full coded VOP area including
> extensions, what would the extended parts contain? Would they contain the
> actual coded information (I assume that there are no requirements to what
> that would be), or should the so-called repetitive padding process of
> section 7.6.1 be applied to the extended parts (although that section begins
> with that the padding process is defined for "...samples outside the VOP for
> prediction of arbitrarily shaped objects")?
> 
> 
> 
> I do hope someone can help me in understanding this better.
> 
> 
> 
> Thanks.
> 
> 
> 
> Jay
> 
> _______________________________________________
> 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.
> 
> Conduct on the mailing list is subject to the Antitrust guidelines 
> found at 
> http://www.mpegif.org/public/documents/vault/mp-out-30042-Antitrust.php

>

Pankaj Kumar Bajpai
Mulitimedia Engineer
India
-- 
_______________________________________________
Surf the Web in a faster, safer and easier way:
Download Opera 9 at http://www.opera.com
Powered by Outblaze