id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc
1619	[Multilayer Profiles] Potential Mismatch of VTM22.0 & Specification Related To Derivation Process For Merge Motion Vector Difference	ksthey		"In ""8.5.2.7 Derivation process for merge motion vector difference"", Equation 563:
mMvdL1[ 0 ] = Sign( currPocDiffL0 ) == Sign( currPocDiffL1 ) ? mMvdL0[ 0 ] : −mMvdL0[ 0 ].

The equivalent code is in VTM22.0, InterPrediction.cpp, MergeCtx::getMmvdDeltaMv(), starting from line 2478:
if ((poc1 - currPoc)*(poc0 - currPoc) > 0)
{
    deltaMv[1] = deltaMv[0];
}
else
{
    deltaMv[1].set(-1 * deltaMv[0].getHor(), -1 * deltaMv[0].getVer());
}

According to specification, definition of Sign(x):
Sign(x) = 1; x > 0
Sign(x) = 0; x == 0
Sign(x) = -1; x < 0

Let's assume:
Result of condition below in specification as r_spec: r_spec = Sign( currPocDiffL0 ) == Sign( currPocDiffL1 )
Result of condition below in VTM22.0 as r_vtm: r_vtm = ((poc1 - currPoc)*(poc0 - currPoc) > 0)

Use combination of currPoc, poc0 & poc1 below as inputs:
1.) currPoc: 1, poc0: 0, poc1: 0
 r_spec = 1; r_vtm = 1;

2.) currPoc: 1, poc0: 0, poc1: 2
 r_spec = 0; r_vtm = 0;

3.) currPoc: 1, poc0: 2, poc1: 0
 r_spec = 0; r_vtm = 0;

4.) currPoc: 1, poc0: 2, poc1: 2
 r_spec = 1; r_vtm = 1;

5.) currPoc: 1, poc0: 1, poc1: 0
 r_spec = 1; r_vtm = 1;

6.) currPoc: 1, poc0: 0, poc1: 1
 r_spec = 1; r_vtm = 1;

7.) currPoc: 1, poc0: 1, poc1: 1
 r_spec = 1; r_vtm = 0;

Case 5, 6 & 7 are only possible in multilayer profiles (current picture and reference picture same POC, but different layers).
As shown above, for case 7, results of specification & VTM are different.
So, which is the correct one? specification or VTM?"	defect	new	minor		VTM			Multilayer	ksuehring XiangLi fbossen jvet@…