lavc/vaapi_h264: Fix merging fields in DPB with missing references

If there are missing references, h264 decode does error concealment
by copying previous refs which means there will be duplicated surfaces.
Check long_ref and frame_idx in addition to surface when looking for
the other field to avoid trying to merge with wrong picture.
Also allow to merge with multiple pictures in case there are duplicates
of the other field.

Signed-off-by: David Rosca <nowrep@gmail.com>
Signed-off-by: Haihao Xiang <haihao.xiang@intel.com>

libavcodec/vaapi_h264.c

@@ -93,14 +93,19 @@ typedef struct DPB {
  */
 static int dpb_add(DPB *dpb, const H264Picture *pic)
 {
-    int i;
+    int i, pic_frame_idx, merged = 0;
 
     if (dpb->size >= dpb->max_size)
         return -1;
 
+    pic_frame_idx = pic->long_ref ? pic->pic_id : pic->frame_num;
+
     for (i = 0; i < dpb->size; i++) {
         VAPictureH264 * const va_pic = &dpb->va_pics[i];
-        if (va_pic->picture_id == ff_vaapi_get_surface_id(pic->f)) {
+        int va_pic_long_ref = !!(va_pic->flags & VA_PICTURE_H264_LONG_TERM_REFERENCE);
+        if (va_pic->picture_id == ff_vaapi_get_surface_id(pic->f) &&
+            va_pic_long_ref == pic->long_ref &&
+            va_pic->frame_idx == pic_frame_idx) {
             VAPictureH264 temp_va_pic;
             fill_vaapi_pic(&temp_va_pic, pic, 0);
 
@@ -112,11 +117,14 @@ static int dpb_add(DPB *dpb, const H264Picture *pic)
                 } else {
                     va_pic->BottomFieldOrderCnt = temp_va_pic.BottomFieldOrderCnt;
                 }
+                merged = 1;
             }
-            return 0;
         }
     }
 
+    if (merged)
+        return 0;
+
     fill_vaapi_pic(&dpb->va_pics[dpb->size++], pic, 0);
     return 0;
 }