swscale: fix crash in bilinear scaling.

libswscale/swscale_internal.h

@@ -194,6 +194,7 @@ typedef struct SwsContext {
 #define Y_TEMP                "11*8+4*4*256*2+40"
 #define ALP_MMX_FILTER_OFFSET "11*8+4*4*256*2+48"
 #define UV_OFF                "11*8+4*4*256*3+48"
+#define UV_OFFx2              "11*8+4*4*256*3+56"
 
     DECLARE_ALIGNED(8, uint64_t, redDither);
     DECLARE_ALIGNED(8, uint64_t, greenDither);
@@ -217,6 +218,7 @@ typedef struct SwsContext {
     DECLARE_ALIGNED(8, uint64_t, y_temp);
     int32_t  alpMmxFilter[4*MAX_FILTER_SIZE];
     DECLARE_ALIGNED(8, ptrdiff_t, uv_off); ///< offset (in pixels) between u and v planes
+    DECLARE_ALIGNED(8, ptrdiff_t, uv_offx2); ///< offset (in bytes) between u and v planes
 
 #if HAVE_ALTIVEC
     vector signed short   CY;

libswscale/utils.c

@@ -1001,6 +1001,7 @@ int sws_init_context(SwsContext *c, SwsFilter *srcFilter, SwsFilter *dstFilter)
         c->lumPixBuf[i] = c->lumPixBuf[i+c->vLumBufSize];
     }
     c->uv_off = dst_stride_px;
+    c->uv_offx2 = dst_stride;
     for (i=0; i<c->vChrBufSize; i++) {
         FF_ALLOC_OR_GOTO(c, c->chrUPixBuf[i+c->vChrBufSize], dst_stride*2+1, fail);
         c->chrUPixBuf[i] = c->chrUPixBuf[i+c->vChrBufSize];