[M4IF Technotes] Interpretation of vop_coded

[Herbert Thoma]

Hi,
the standard (ISO/IEC 14496-2:1999/Amd.1:2000) says in section 6.3.5:
"vop_coded: This is a 1-bit flag which when set to '0' indicates that no subsequent
data exists for the VOP. (...) If binary shape or alpha plane does not exist for the VOP 
(i.e. video_object_layer_shape == "rectangular"), the luminance and chrominance planes of
the reconstructed VOP shall be filled with the forward reference VOP as defined in
subclause 7.6.7."
In my opinion this means: copy the previous VOP.
If the Microsoft reference code behaves like you described, thers is a
discrepancy between the Microsoft reference code and the standard text.
Regards,
 Herbert.
Yogendra Kumar Gupta wrote:
> 
> Dear All,
> 
> Can anyone please explain the interpretation of the flag vop_coded (when
> vop_coded = 0) when video_object_layer_shape == RECTANGULAR. The standard
> gives details of the construction of reconstructed frame but does not give
> any interpretation regarding the construction of the current frame (that
> would be used for display). The Microsoft reference code puts a grey image
> of colour 128 in the o/p which doesn't look very nice in between while
> watching a video. One of the conformance bitstreams contains frames where
> every alternate frame the flag vop_coded is set to 0 and the o/p looks like
> a blinking one where you get a decoded image and a gray image alternatively.
> Could a better solution be use the previous frame itself for display when
> vop_coded = 0. Also I would like to know when the flag vop_coded needs to be
> set to 0 on the encoding side.
> 
> Regards
> Yogender Kumar Gupta
> 
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Herbert Thoma
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