avcodec/vaapi: do not parse MVMODE for VC-1 interlaced frame pictures

Interlaced frame pictures do not contain the MVMODE or MVMODE2 bitstream
element. Trying to parse this element and passing a nonzero value to the
hardware decoder results in small inaccuracies in the decoded picture.
Signed-off-by: Jerome Borsboom <jerome.borsboom@carpalis.nl>

libavcodec/vaapi_vc1.c

@@ -138,8 +138,9 @@ static int vc1_get_FPTYPE(const VC1Context *v)
 /** Reconstruct bitstream MVMODE (7.1.1.32) */
 static inline VAMvModeVC1 vc1_get_MVMODE(const VC1Context *v)
 {
-    if ((v->s.pict_type == AV_PICTURE_TYPE_P && !v->p_frame_skipped) ||
-        (v->s.pict_type == AV_PICTURE_TYPE_B && !v->bi_type))
+    if ((v->fcm == PROGRESSIVE || v->fcm == ILACE_FIELD) &&
+        ((v->s.pict_type == AV_PICTURE_TYPE_P && !v->p_frame_skipped) ||
+         (v->s.pict_type == AV_PICTURE_TYPE_B && !v->bi_type)))
         return get_VAMvModeVC1(v->mv_mode);
     return 0;
 }
@@ -147,7 +148,8 @@ static inline VAMvModeVC1 vc1_get_MVMODE(const VC1Context *v)
 /** Reconstruct bitstream MVMODE2 (7.1.1.33) */
 static inline VAMvModeVC1 vc1_get_MVMODE2(const VC1Context *v)
 {
-    if ((v->s.pict_type == AV_PICTURE_TYPE_P && !v->p_frame_skipped) &&
+    if ((v->fcm == PROGRESSIVE || v->fcm == ILACE_FIELD) &&
+        (v->s.pict_type == AV_PICTURE_TYPE_P && !v->p_frame_skipped) &&
         v->mv_mode == MV_PMODE_INTENSITY_COMP)
         return get_VAMvModeVC1(v->mv_mode2);
     return 0;