Correct some rounding errors introduced recently.

media/base/video_frame.cc

Index: media/base/video_frame.cc
===================================================================
--- media/base/video_frame.cc	(revision 109319)
+++ media/base/video_frame.cc	(working copy)
@@ -118,10 +118,10 @@
   // to avoid any potential of faulting by code that attempts to access the Y
   // values of the final row, but assumes that the last row of U & V applies to
   // a full two rows of Y.
-  size_t y_height = RoundUp(rows(VideoFrame::kYPlane), 2);
+  size_t y_height = rows(VideoFrame::kYPlane);

[scherkus (not reviewing), 2011/11/10 04:09:41]

this change looks OK and avoids over-allocating one extra row

   size_t y_stride = RoundUp(row_bytes(VideoFrame::kYPlane), 4);
   size_t uv_stride = RoundUp(row_bytes(VideoFrame::kUPlane), 4);
-  size_t uv_height = RoundUp(rows(VideoFrame::kUPlane), 2);
+  size_t uv_height = rows(VideoFrame::kUPlane);
   size_t y_bytes = y_height * y_stride;
   size_t uv_bytes = uv_height * uv_stride;
 
@@ -195,7 +195,7 @@
     case YV16:
       if (plane == kYPlane)
         return width_;
-      return width_ / 2;
+      return RoundUp(width_, 2) / 2;

[scherkus (not reviewing), 2011/11/10 04:09:41]

so we're always rounding up post-divide?

i.e., this should be equivalent to (width_ / 2) | 0x1

[Chris Evans, 2011/11/10 06:32:38]

The intent is to round up pre-divide -- the divide is executed on the return
value of RoundUp. (The old way was to round up post-divide and that led to the
under-allocation issues).
More like (width_ / 2) + (width_ & 1)

The way I conceptualized these changes is to imagine a 1x1 video frame. We need
to allocate at least 1x1 of working space, even for planes that are scaled by
half on both the horiz and vert dimensions.

 
     default:
       break;
@@ -220,7 +220,7 @@
     case YV12:
       if (plane == kYPlane)
         return height_;
-      return height_ / 2;
+      return RoundUp(height_, 2) / 2;
 
     default:
       break;