@@ -3148,7 +3148,7 @@ static int decode_slice_header(H264Context *h, H264Context *h0)

     int must_reinit;

     int needs_reinit = 0;

     int first_slice = h == h0 && !h0->current_slice;

-    int frame_num;

+    int frame_num, picture_structure, droppable;

     PPS *pps;

     h->me.qpel_put = h->h264qpel.put_h264_qpel_pixels_tab;

@@ -3342,37 +3342,32 @@ static int decode_slice_header(H264Context *h, H264Context *h0)

             return AVERROR_INVALIDDATA;

         }

     }

-    h->frame_num = frame_num;

     h->mb_mbaff        = 0;

     h->mb_aff_frame    = 0;

     last_pic_structure = h0->picture_structure;

     last_pic_droppable = h0->droppable;

-    h->droppable       = h->nal_ref_idc == 0;

+    droppable          = h->nal_ref_idc == 0;

     if (h->sps.frame_mbs_only_flag) {

-        h->picture_structure = PICT_FRAME;

+        picture_structure = PICT_FRAME;

     } else {

         if (!h->sps.direct_8x8_inference_flag && slice_type == AV_PICTURE_TYPE_B) {

             av_log(h->avctx, AV_LOG_ERROR, "This stream was generated by a broken encoder, invalid 8x8 inference\n");

             return -1;

         }

         if (get_bits1(&h->gb)) { // field_pic_flag

-            h->picture_structure = PICT_TOP_FIELD + get_bits1(&h->gb); // bottom_field_flag

+            picture_structure = PICT_TOP_FIELD + get_bits1(&h->gb); // bottom_field_flag

         } else {

-            h->picture_structure = PICT_FRAME;

+            picture_structure = PICT_FRAME;

             h->mb_aff_frame      = h->sps.mb_aff;

         }

     }

-    h->mb_field_decoding_flag = h->picture_structure != PICT_FRAME;

-

-    if (h0->current_slice != 0) {

-        if (last_pic_structure != h->picture_structure ||

-            last_pic_droppable != h->droppable) {

+    if (h0->current_slice) {

+        if (last_pic_structure != picture_structure ||

+            last_pic_droppable != droppable) {

             av_log(h->avctx, AV_LOG_ERROR,

                    "Changing field mode (%d -> %d) between slices is not allowed\n",

                    last_pic_structure, h->picture_structure);

-            h->picture_structure = last_pic_structure;

-            h->droppable         = last_pic_droppable;

             return AVERROR_INVALIDDATA;

         } else if (!h0->cur_pic_ptr) {

             av_log(h->avctx, AV_LOG_ERROR,

@@ -3380,7 +3375,14 @@ static int decode_slice_header(H264Context *h, H264Context *h0)

                    h0->current_slice + 1);

             return AVERROR_INVALIDDATA;

         }

-    } else {

+    }

+

+    h->picture_structure = picture_structure;

+    h->droppable         = droppable;

+    h->frame_num         = frame_num;

+    h->mb_field_decoding_flag = picture_structure != PICT_FRAME;

+

+    if (h0->current_slice == 0) {

         /* Shorten frame num gaps so we don't have to allocate reference

          * frames just to throw them away */

         if (h->frame_num != h->prev_frame_num) {