[FFmpeg-devel] [PATCH] lavc/vvc: Read subpic ID when only one subpicture is present

[Frank Plowman <post@frankplowman.com>]

Previously, the following syntax elements were not read in the case
sps_num_subpics_minus is 0:
* sps_subpic_id_len_minus1
* sps_subpic_id_mapping_explicitly_signalled_flag
* sps_subpic_id_mapping_present_flag
* sps_subpic_id[i]
This was causing failures to decode bitstreams, for example the DVB's
"VVC HDR UHDTV1 OpenGOP 3840x2160 50fps HLG10 PiP" V&V bitstream.

Patch fixes this by moving the reads for these syntax elements out a
scope.

Signed-off-by: Frank Plowman <post@frankplowman.com>
---
Sorry, should probably have put this in with
53ab7ff67e7ee9e7cae5cb0449203a7951cbe029.

 libavcodec/cbs_h266_syntax_template.c | 36 +++++++++++++--------------
 1 file changed, 18 insertions(+), 18 deletions(-)

diff --git a/libavcodec/cbs_h266_syntax_template.c b/libavcodec/cbs_h266_syntax_template.c
index 1d4d0c796f..623417fce4 100644
--- a/libavcodec/cbs_h266_syntax_template.c
+++ b/libavcodec/cbs_h266_syntax_template.c
@@ -1213,30 +1213,30 @@ static int FUNC(sps)(CodedBitstreamContext *ctx, RWContext *rw,
                     infer(sps_loop_filter_across_subpic_enabled_flag[i], 0);
                 }
             }
-            ue(sps_subpic_id_len_minus1, 0, 15);
-            if ((1 << (current->sps_subpic_id_len_minus1 + 1)) <
-                current->sps_num_subpics_minus1 + 1) {
-                av_log(ctx->log_ctx, AV_LOG_ERROR,
-                       "sps_subpic_id_len_minus1(%d) is too small\n",
-                       current->sps_subpic_id_len_minus1);
-                return AVERROR_INVALIDDATA;
-            }
-            flag(sps_subpic_id_mapping_explicitly_signalled_flag);
-            if (current->sps_subpic_id_mapping_explicitly_signalled_flag) {
-                flag(sps_subpic_id_mapping_present_flag);
-                if (current->sps_subpic_id_mapping_present_flag) {
-                    for (i = 0; i <= current->sps_num_subpics_minus1; i++) {
-                        ubs(current->sps_subpic_id_len_minus1 + 1,
-                            sps_subpic_id[i], 1, i);
-                    }
-                }
-            }
         } else {
             infer(sps_subpic_ctu_top_left_x[0], 0);
             infer(sps_subpic_ctu_top_left_y[0], 0);
             infer(sps_subpic_width_minus1[0], tmp_width_val - 1);
             infer(sps_subpic_height_minus1[0], tmp_height_val - 1);
         }
+        ue(sps_subpic_id_len_minus1, 0, 15);
+        if ((1 << (current->sps_subpic_id_len_minus1 + 1)) <
+            current->sps_num_subpics_minus1 + 1) {
+            av_log(ctx->log_ctx, AV_LOG_ERROR,
+                   "sps_subpic_id_len_minus1(%d) is too small\n",
+                   current->sps_subpic_id_len_minus1);
+            return AVERROR_INVALIDDATA;
+        }
+        flag(sps_subpic_id_mapping_explicitly_signalled_flag);
+        if (current->sps_subpic_id_mapping_explicitly_signalled_flag) {
+            flag(sps_subpic_id_mapping_present_flag);
+            if (current->sps_subpic_id_mapping_present_flag) {
+                for (i = 0; i <= current->sps_num_subpics_minus1; i++) {
+                    ubs(current->sps_subpic_id_len_minus1 + 1,
+                        sps_subpic_id[i], 1, i);
+                }
+            }
+        }
     } else {
         infer(sps_num_subpics_minus1, 0);
         infer(sps_independent_subpics_flag, 1);
-- 
2.43.2

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