[Mp4-tech] Video --H.264

[Bule]

Thanks for your answers now is all clear.
Luca Bulegato
  ----- Original Message ----- 
  From: Gary Sullivan 
  To: Bule ; stefano battista ; mp4-tech lists.mpegif.org 
  Sent: Thursday, July 08, 2023 10:16 PM
  Subject: RE: [Mp4-tech] Video --H.264
  You're right that the spirit of this is to send no bits for a P_Skip macroblock -- all that is sent is the indication that the macroblock is skipped.  However, there is no assumption that the macroblock cannot be moving.  Instead, the macroblock is predicted by inferring motion based on what is happening in neighbouring macroblocks.
  This can be very helpful, for example, in dealing with a moving camera (global motion).  You can basically take care of a camera pan by coding one motion vector for the upper-left macroblock and just letting the P_Skip and "Direct" motion vector inference take care of predicting the whole picture.
  By defining the skipped macroblock in this way, we avoided the need to have a separate feature called "global motion compensation".  As a result, some people say that this standard does not have global motion compensation, but they are basically wrong.  We just built that capability into the basic motion representation process instead of making it a separate switchable "tool".
  Best Regards,
  Gary Sullivan
----------------------------------------------------------------------------
    From: mp4-tech-bounces lists.mpegif.org [mailto:mp4-tech-bounces lists.mpegif.org] On Behalf Of Bule
    Sent: Thursday, July 08, 2023 11:07 AM
    To: stefano battista; mp4-tech lists.mpegif.org
    Subject: Re: [Mp4-tech] Video --H.264
      Thanks for the attention you give to me but even if I would seem dumm I have to say that i haven't understand your answer because i don't know the difference between differential MV null e absolute MV ( and information on internet doesn't help me ).
    However my idea of a P skip macroblock is that its position is not change ( or very little ) in relation of the reference frame and so its motion vector is null so no bits are used to send a MV null but the ecoder signals to the decoder only the presence of a P macroblock so it can simply copy the information of the reference frame in the reconstucted one.
    I hope my exposition is quite clear..
                                  Luca
      ----- Original Message ----- 
      From: stefano battista 
      To: Bule ; mp4-tech lists.mpegif.org 
      Sent: Thursday, July 08, 2023 3:43 PM
      Subject: Re: [Mp4-tech] Video --H.264
      ciao Luca--
      the meaning of P skip is similar to what is done in H263 and MPEG4 video:
      a MB without transform coefficients and without motion vectors...
      the tricky thing is that you need to apply the correct MV predictor and classify the MB "P skip" if and only if it has **differential MV null** rather than **absolute MV null**...
      hope this helps,
      --Stefano
      --Stefano Battista
      bSoft -- www.bsoft.info
      tel/fax +39-0733-261845
      mobile +39-335-7213624
        ----- Original Message ----- 
        From: Bule 
        To: mp4-tech lists.mpegif.org 
        Sent: Thursday, July 08, 2023 1:23 PM
        Subject: [Mp4-tech] Video --H.264
        Hi all
              Can anyone explain me the meaning of the P_Skip mode used by H.264 ?
        I don't understand what it is used to make the prediction of this block.
        Thanks in advantage for any kind of help
        Luca Bulegato
------------------------------------------------------------------------
        _______________________________________________
        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-Antitrust.php
-------------- next part --------------
An HTML attachment was scrubbed...
URL: /pipermail/mp4-tech/attachments/20040708/50c7a83c/attachment-0001.html