[M4IF Technotes] Offscreen MVs

[Peter Haighton]

Graham,
Yes, it is possible for a motion vector to point off the screen. The off
screen pixels are duplicated from the edge of the on screen pixels.
Peter
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Sent: Monday, May 20, 2024 1:22 PM
To: technotes   lists.m4if.org
Subject: [M4IF Technotes] Offscreen MVs
 Is it possible to have a motion vector to point outside the screen? I
know
you can point outside a VOP (with long header only if I remember
correctly),
but off-screen?
Say there is a feature at position (0,0) in frame 1 (F1) and in F2 that
feature moves up by 1 pixel so that we lose the top row.
What I'd like to do is to signal the decoder a motion vector of (0,-1),
but
the decoder would then need to know what pixels to put in the bottom row
of
the macroblock in F2.
I could always just pass a MV of (0,0) buit if we take the worst case
whereby every row of that feature had a different luminance value (eg
stripped) then I would get a larger error value than if I sent a MV of
(0,-1) and the decoder put in some random pixels into the lowest row of
that
macroblock.
I don't think I can pass MVs that point off screen but I thought I'd
check.
regards
Graham
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