[Mp4-tech] MPEG-4 Visual conformance bitstream problem

[sunx]

The function "limitMVRangeToExtendedBBHalfPel()" should limit the motion
vectors within the legal range. If the MVs are going to be out of range,
then they will be truncated.
On Tue, 11 Nov 2023 toshi.horie conexant.com wrote:
> I have found a problem with the motion vectors on the
> following MPEG-4 visual V1 Simple Profile short header
> conformance bitstreams:
>
> Name        Resolution  Frames  Profile Level
> san021.m4v   352x288      99      Simple L2
> san022.m4v   176x144     100      Simple L1
> san023.m4v   352x288      49      Simple L2
> san024.m4v   352x288     127      Simple L3
>
> These bitstreams have have unrestricted motion vectors even though
> 14496-2, section 7.6.4 says "Motion vectors are allowed to point
> outside the decoded area of a reference VOP when (and only when)
> the short video header format is not in use (i.e., when
> short_video_header is 0)."
>
> For example, on san021.m4v on the third VOP at macroblock 110,
> vop=2 MB=110 comp=0 (refx,refy)=(-5,72) horiz out of range
> vop=2 MB=110 comp=2 (refx,refy)=(-5,80) horiz out of range
> vop=2 MB=110 comp=4 (refx,refy)=(-3,36) horiz out of range
>
> Best Regards,
> Toshi Horie
>