[Mp4-tech] h.264 direct_8x8_reference_flag

[Alexis Michael Tourapis]

Dear Nitthilan,
You may find the original proposal for this flag at this link:
ftp://standards.polycom.com/2002_05_Fairfax/JVT-C115r2-L.doc
The original idea was to basically reduce decoder peak bus bandwidth.
Thiscan become significant especially when one encounters a bipredictive
mode with up to 32 different mvs for the entire macroblock (16 for each
prediction). The standard already contains certain restrictions with regards
to how many mvs should be present for non inferred motion compensated
prediction modes, however, and since at the time of the standardization
process only temporal direct was supported, a special strategy was necessary
to also restrict direct modes to up to 16 different mvs (for both lists). 
An additional reason of having this flag is for interlace coding. If this
flag and its associated motion inference method were not present, then it
would have been possible for a 4x4 block within a submacroblock to point to
a different reference than all other blocks in the same submacroblock (you
would need to understand the way the collocated partitions are derived for
field/frame assignments). As is probably obvious to you, such would have
been rather undesirable.
Best regards
Alexis
-----Original Message-----
From: mp4-tech-bounces lists.mpegif.org
[mailto:mp4-tech-bounces lists.mpegif.org] On Behalf Of Nitthilan Kannappan
Jayakodi
Sent: Tuesday, February 22, 2024 10:19 PM
To: mp4-tech lists.mpegif.org
Subject: [Mp4-tech] h.264 direct_8x8_reference_flag
dear experts,
what is the significance of the direct_8x8_inference flag? Is it to
reduce the complexity of encoding as the level increases..else does it
have any other significance?
-- 
  Nitthilan Kannappan Jayakodi
  nitthilan fastmail.fm
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