h264: decode the poc values from the slice header into the per-slice context

Copy them into the decoder-global context in field_start(). This avoids
modifying the decoder-global context during bitstream parsing.

libavcodec/h264.h

@@ -446,6 +446,11 @@ typedef struct H264SliceContext {
     MMCO mmco[MAX_MMCO_COUNT];
     int  nb_mmco;
     int explicit_ref_marking;
+
+    int frame_num;
+    int poc_lsb;
+    int delta_poc_bottom;
+    int delta_poc[2];
 } H264SliceContext;
 
 /**

libavcodec/h264_slice.c

@@ -1009,6 +1009,12 @@ static int h264_field_start(H264Context *h, const H264SliceContext *sl,
     h->droppable         = (nal->ref_idc == 0);
     h->picture_structure = sl->picture_structure;
 
+    h->poc.frame_num        = sl->frame_num;
+    h->poc.poc_lsb          = sl->poc_lsb;
+    h->poc.delta_poc_bottom = sl->delta_poc_bottom;
+    h->poc.delta_poc[0]     = sl->delta_poc[0];
+    h->poc.delta_poc[1]     = sl->delta_poc[1];
+
     /* Shorten frame num gaps so we don't have to allocate reference
      * frames just to throw them away */
     if (h->poc.frame_num != h->poc.prev_frame_num) {
@@ -1175,7 +1181,7 @@ static int h264_slice_header_parse(H264Context *h, H264SliceContext *sl,
     int ret;
     unsigned int slice_type, tmp, i;
     int field_pic_flag, bottom_field_flag;
-    int frame_num, droppable, picture_structure;
+    int droppable, picture_structure;
 
     sl->first_mb_addr = get_ue_golomb(&sl->gb);
 
@@ -1222,9 +1228,7 @@ static int h264_slice_header_parse(H264Context *h, H264SliceContext *sl,
     }
     sps = (const SPS*)h->ps.sps_list[pps->sps_id]->data;
 
-    frame_num = get_bits(&sl->gb, sps->log2_max_frame_num);
-    if (!h->setup_finished)
-        h->poc.frame_num = frame_num;
+    sl->frame_num = get_bits(&sl->gb, sps->log2_max_frame_num);
 
     sl->mb_mbaff       = 0;
 
@@ -1244,10 +1248,10 @@ static int h264_slice_header_parse(H264Context *h, H264SliceContext *sl,
     sl->mb_field_decoding_flag = picture_structure != PICT_FRAME;
 
     if (picture_structure == PICT_FRAME) {
-        h->curr_pic_num = h->poc.frame_num;
+        h->curr_pic_num = sl->frame_num;
         h->max_pic_num  = 1 << sps->log2_max_frame_num;
     } else {
-        h->curr_pic_num = 2 * h->poc.frame_num + 1;
+        h->curr_pic_num = 2 * sl->frame_num + 1;
         h->max_pic_num  = 1 << (sps->log2_max_frame_num + 1);
     }
 
@@ -1255,30 +1259,17 @@ static int h264_slice_header_parse(H264Context *h, H264SliceContext *sl,
         get_ue_golomb(&sl->gb); /* idr_pic_id */
 
     if (sps->poc_type == 0) {
-        int poc_lsb = get_bits(&sl->gb, sps->log2_max_poc_lsb);
-
-        if (!h->setup_finished)
-            h->poc.poc_lsb = poc_lsb;
+        sl->poc_lsb = get_bits(&sl->gb, sps->log2_max_poc_lsb);
 
-        if (pps->pic_order_present == 1 && picture_structure == PICT_FRAME) {
-            int delta_poc_bottom = get_se_golomb(&sl->gb);
-            if (!h->setup_finished)
-                h->poc.delta_poc_bottom = delta_poc_bottom;
-        }
+        if (pps->pic_order_present == 1 && picture_structure == PICT_FRAME)
+            sl->delta_poc_bottom = get_se_golomb(&sl->gb);
     }
 
     if (sps->poc_type == 1 && !sps->delta_pic_order_always_zero_flag) {
-        int delta_poc = get_se_golomb(&sl->gb);
+        sl->delta_poc[0] = get_se_golomb(&sl->gb);
 
-        if (!h->setup_finished)
-            h->poc.delta_poc[0] = delta_poc;
-
-        if (pps->pic_order_present == 1 && picture_structure == PICT_FRAME) {
-            delta_poc = get_se_golomb(&sl->gb);
-
-            if (!h->setup_finished)
-                h->poc.delta_poc[1] = delta_poc;
-        }
+        if (pps->pic_order_present == 1 && picture_structure == PICT_FRAME)
+            sl->delta_poc[1] = get_se_golomb(&sl->gb);
     }
 
     if (pps->redundant_pic_cnt_present)