win32 contribs: Fix dxva2 decoding for Intel cards

Tested on GMA HD, ATI/NVIDIA
Untested on GMA4500

Needs testing on more cards and samples before it is committed upstream

extras/contrib/src/Makefile

@@ -1057,6 +1057,7 @@ ifdef HAVE_UCLIBC
 	patch -p0 < Patches/ffmpeg-svn-libavformat.patch
 endif
 ifdef HAVE_WIN32
+	patch -p0 < Patches/ffmpeg-dxva2_h264.patch
 	sed -i "s/std=c99/std=gnu99/" ffmpeg/configure
 endif
 else

extras/contrib/src/Patches/ffmpeg-dxva2_h264.patch

+diff -u ffmpeg/libavcodec/dxva2_h264.c ffmpeg/libavcodec/dxva2_h264.c
+--- ffmpeg/libavcodec/dxva2_h264.c
++++ ffmpeg/libavcodec/dxva2_h264.c
+@@ -194,7 +194,7 @@ static void fill_slice_long(AVCodecContext *avctx, DXVA_Slice_H264_Long *slice,
+ 
+     slice->first_mb_in_slice     = (s->mb_y >> FIELD_OR_MBAFF_PICTURE) * s->mb_width + s->mb_x;
+     slice->NumMbsForSlice        = 0; /* XXX it is set once we have all slices */
+-    slice->BitOffsetToSliceData  = get_bits_count(&s->gb) + 8;
++    slice->BitOffsetToSliceData  = get_bits_count(&s->gb);
+     slice->slice_type            = ff_h264_get_slice_type(h);
+     if (h->slice_type_fixed)
+         slice->slice_type += 5;