dxva2_h264: add a workaround for old intel GPUs

Old Intel GPUs expect the reference frame index to the actual surface,
instead of the index into RefFrameList as specified by the spec.

This workaround should be set when using one of the "ClearVideo" decoder
devices.
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/dxva2.h

@@ -49,6 +49,7 @@
  */
 
 #define FF_DXVA2_WORKAROUND_SCALING_LIST_ZIGZAG 1 ///< Work around for DXVA2 and old UVD/UVD+ ATI video cards
+#define FF_DXVA2_WORKAROUND_INTEL_CLEARVIDEO    2 ///< Work around for DXVA2 and old Intel GPUs with ClearVideo interface
 
 /**
  * This structure is used to provides the necessary configurations and data

libavcodec/dxva2_h264.c

@@ -115,6 +115,8 @@ static void fill_picture_parameters(struct dxva_context *ctx, const H264Context
     pp->bit_depth_chroma_minus8       = h->sps.bit_depth_chroma - 8;
     if (ctx->workaround & FF_DXVA2_WORKAROUND_SCALING_LIST_ZIGZAG)
         pp->Reserved16Bits            = 0;
+    else if (ctx->workaround & FF_DXVA2_WORKAROUND_INTEL_CLEARVIDEO)
+        pp->Reserved16Bits            = 0x34c;
     else
         pp->Reserved16Bits            = 3; /* FIXME is there a way to detect the right mode ? */
     pp->StatusReportFeedbackNumber    = 1 + ctx->report_id++;
@@ -238,7 +240,11 @@ static void fill_slice_long(AVCodecContext *avctx, DXVA_Slice_H264_Long *slice,
             if (list < h->list_count && i < h->ref_count[list]) {
                 const Picture *r = &h->ref_list[list][i];
                 unsigned plane;
-                unsigned index = get_refpic_index(pp, ff_dxva2_get_surface_index(ctx, r));
+                unsigned index;
+                if (ctx->workaround & FF_DXVA2_WORKAROUND_INTEL_CLEARVIDEO)
+                    index = ff_dxva2_get_surface_index(ctx, r);
+                else
+                    index = get_refpic_index(pp, ff_dxva2_get_surface_index(ctx, r));
                 fill_picture_entry(&slice->RefPicList[list][i], index,
                                    r->reference == PICT_BOTTOM_FIELD);
                 for (plane = 0; plane < 3; plane++) {