[Mp4-tech] Mpeg4V2 Vs Divx5.0.5 in B-VOP Motion Coding

[sunx]

I think either (1) Divx5.0.5 does not support the BVOP or (2) it supports
a special combination sequence of I,P,B frames, e.g., IPBP is supported
but IPPBPP is not supported. Even for the baseline profile of MPEG-4, Divx
does not implement all the coding modes.
On Thu, 4 Dec 2003, [gb2312] ºúÖ¾ÐÛ wrote:
> Dear All,
>        MPEG-4V2 Motion Vector Coding in B-VOP is:
>  	   Motion vectors are to be coded differentially. Only vectors that are used for the    selected prediction mode are actually coded. For forward and backward motion vectors in forward, backward and bidirectional mode the left neighboring vector of the same direction type is used as predictor. In case the current macroblock is located on the left edge of the VOP or no vector of the same direction type is present, the predictor is set to zero.
>        Is it different between Divx5.0.5 and MPEG4V2?
>        Because I had write a decoder for MPEG-4 ASP stream,when decode standard MPEG-4 (include B-VOP)stream,decoder is right,but when it decode the stream generate by DIVX5.0.5,
> I-VOP and P-VOP is right,something wrong in decoding B-VOP.
>        Does any one tell me some information?
>        Thanks a lot!¡¡¡¡¡¡¡¡¡¡¡¡¡¡
>
>        Dennis
>
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