change scale down by 4 to use rounding.

source/scale.cc

 /*
  *  Copyright 2011 The LibYuv Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS. All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 164 matching lines @@
   }
 #if defined(HAS_SCALEROWDOWN4_NEON)
   if (TestCpuFlag(kCpuHasNEON)) {
     ScaleRowDown4 = filtering ?
         ScaleRowDown4Box_Any_NEON : ScaleRowDown4_Any_NEON;
     if (IS_ALIGNED(dst_width, 8)) {
       ScaleRowDown4 = filtering ? ScaleRowDown4Box_NEON : ScaleRowDown4_NEON;
     }
   }
 #endif
-#if defined(HAS_SCALEROWDOWN4_SSE2)
-  if (TestCpuFlag(kCpuHasSSE2)) {
+#if defined(HAS_SCALEROWDOWN4_SSSE3)
+  if (TestCpuFlag(kCpuHasSSSE3)) {
     ScaleRowDown4 = filtering ?
-        ScaleRowDown4Box_Any_SSE2 : ScaleRowDown4_Any_SSE2;
+        ScaleRowDown4Box_Any_SSSE3 : ScaleRowDown4_Any_SSSE3;
     if (IS_ALIGNED(dst_width, 8)) {
-      ScaleRowDown4 = filtering ? ScaleRowDown4Box_SSE2 : ScaleRowDown4_SSE2;
+      ScaleRowDown4 = filtering ? ScaleRowDown4Box_SSSE3 : ScaleRowDown4_SSSE3;
     }
   }
 #endif
 #if defined(HAS_SCALEROWDOWN4_AVX2)
   if (TestCpuFlag(kCpuHasAVX2)) {
     ScaleRowDown4 = filtering ?
         ScaleRowDown4Box_Any_AVX2 : ScaleRowDown4_Any_AVX2;
     if (IS_ALIGNED(dst_width, 16)) {
       ScaleRowDown4 = filtering ? ScaleRowDown4Box_AVX2 : ScaleRowDown4_AVX2;
     }
@@ skipping 1479 matching lines @@
                    dst_u, dst_halfwidth,
                    dst_v, dst_halfwidth,
                    dst_width, aheight,
                    interpolate ? kFilterBox : kFilterNone);
 }
 
 #ifdef __cplusplus
 }  // extern "C"
 }  // namespace libyuv
 #endif