Fix sliced yuv410 -> yuv420 conversion

Originally committed as revision 29272 to svn://svn.mplayerhq.hu/mplayer/trunk/libswscale

libswscale/swscale.c

@@ -2108,11 +2108,15 @@ static int yvu9toyv12Wrapper(SwsContext *c, uint8_t* src[], int srcStride[], int
     }
 
     if (c->dstFormat==PIX_FMT_YUV420P || c->dstFormat==PIX_FMT_YUVA420P){
-        planar2x(src[1], dst[1], c->chrSrcW, c->chrSrcH, srcStride[1], dstStride[1]);
-        planar2x(src[2], dst[2], c->chrSrcW, c->chrSrcH, srcStride[2], dstStride[2]);
+        planar2x(src[1], dst[1] + dstStride[1]*(srcSliceY >> 1), c->chrSrcW,
+                 srcSliceH >> 2, srcStride[1], dstStride[1]);
+        planar2x(src[2], dst[2] + dstStride[2]*(srcSliceY >> 1), c->chrSrcW,
+                 srcSliceH >> 2, srcStride[2], dstStride[2]);
     }else{
-        planar2x(src[1], dst[2], c->chrSrcW, c->chrSrcH, srcStride[1], dstStride[2]);
-        planar2x(src[2], dst[1], c->chrSrcW, c->chrSrcH, srcStride[2], dstStride[1]);
+        planar2x(src[1], dst[2] + dstStride[2]*(srcSliceY >> 1), c->chrSrcW,
+                 srcSliceH >> 2, srcStride[1], dstStride[2]);
+        planar2x(src[2], dst[1] + dstStride[1]*(srcSliceY >> 1), c->chrSrcW,
+                 srcSliceH >> 2, srcStride[2], dstStride[1]);
     }
     if (dst[3])
         fillPlane(dst[3], dstStride[3], c->srcW, srcSliceH, srcSliceY, 255);