[x265] [PATCH] Improve Slices option with check zeroMv

[Richard]

Zero MV is only one special case of the problem.


The code of MV restriction calculation:
    tld.analysis.m_sliceMinY = -(int32_t)(rowInSlice * m_param->maxCUSize * 4) + 3 * 4;
    tld.analysis.m_sliceMaxY = (int32_t)((endRowInSlicePlus1 - 1 - row) * (m_param->maxCUSize * 4) - 4 * 4);


The constants will cause MVs to be restricted to >12 or <-16 in slice boundaries.
example:
    minY: -2036, maxY: -16
or
    minY: 12, maxY: 1776
So any MV that has its Y-axis in the range of -16 to 12 will have problem.


         Original
         
       




From baff7691e9bc4f93bccc85ae78d95ad9ade7a8d0 Mon Sep 17 00:00:00 2001  From: Min Chen <chenm003 at 163.com>
 Date: Fri, 14 Mar 2025 22:27:02 -0700
 Subject: [PATCH] Improve Slices option with check zeroMv

 
 ---
  source/encoder/analysis.cpp | 4 ++--
  source/encoder/motion.cpp   | 8 ++++++++
  2 files changed, 10 insertions(+), 2 deletions(-)

 
 diff --git a/source/encoder/analysis.cpp b/source/encoder/analysis.cpp
 index 5475e4800..e3c410e59 100644
 --- a/source/encoder/analysis.cpp
 +++ b/source/encoder/analysis.cpp
 @@ -3166,7 +3166,7 @@ void Analysis::checkMerge2Nx2N_rd0_4(Mode& skip, Mode& merge, const CUGeom& cuGe
      }
      for (uint32_t i = 0; i < numMergeCand; ++i)
      {
 -        if (m_bFrameParallel)
 +        if (m_bFrameParallel && candMvField[i][0].mv.notZero())
          {
              // Parallel slices bound check
              if (m_param->maxSlices > 1)
 @@ -3300,7 +3300,7 @@ void Analysis::checkMerge2Nx2N_rd5_6(Mode& skip, Mode& merge, const CUGeom& cuGe
      }
      for (uint32_t i = 0; i < numMergeCand; i++)
      {
 -        if (m_bFrameParallel)
 +        if (m_bFrameParallel && candMvField[i][0].mv.notZero())
          {
              // Parallel slices bound check
              if (m_param->maxSlices > 1)
 diff --git a/source/encoder/motion.cpp b/source/encoder/motion.cpp
 index 58e943652..86f413c3d 100644
 --- a/source/encoder/motion.cpp
 +++ b/source/encoder/motion.cpp
 @@ -1596,6 +1596,14 @@ me_hex2:
      // check mv range for slice bound
      X265_CHECK(((bmv.y >= qmvmin.y) & (bmv.y <= qmvmax.y)), "mv beyond range!");
  
 +    // Get a chance to ZeroMv
 +    if (bmv.notZero())
 +    {
 +      int cost = subpelCompare(ref, MV(0, 0), satd) + mvcost(MV(0, 0));
 +      if (cost <= bcost)
 +        bmv = MV(0, 0);
 +    }
 +
      x265_emms();
      outQMv = bmv;
      return bcost;
 -- 
 2.43.0.windows.1
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