dxva2: Increase maximum number of slices for mpeg2

Some content requires an higher number of slices in order to
render properly.

Rise the number to 1024 and warn if ever it exceeds.

Signed-off-by: Luca Barbato <lu_zero@gentoo.org>

libavcodec/dxva2_mpeg2.c

@@ -20,9 +20,10 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
+#include "libavutil/log.h"
 #include "dxva2_internal.h"
 
-#define MAX_SLICES (SLICE_MAX_START_CODE - SLICE_MIN_START_CODE + 1)
+#define MAX_SLICES 1024
 struct dxva2_picture_context {
     DXVA_PictureParameters pp;
     DXVA_QmatrixData       qm;
@@ -233,9 +234,11 @@ static int dxva2_mpeg2_decode_slice(AVCodecContext *avctx,
         s->current_picture_ptr->hwaccel_picture_private;
     unsigned position;
 
-    if (ctx_pic->slice_count >= MAX_SLICES)
+    if (ctx_pic->slice_count >= MAX_SLICES) {
+        avpriv_request_sample(avctx, "%d slices in dxva2",
+                              ctx_pic->slice_count);
         return -1;
-
+    }
     if (!ctx_pic->bitstream)
         ctx_pic->bitstream = buffer;
     ctx_pic->bitstream_size += size;