[FFmpeg-devel] [PATCH 03/11] mpeg2_metadata, cbs_mpeg2: Fix handling of colour_description

[Andreas Rheinhardt]

If a sequence display extension is read with colour_description equal to
zero, but a user wants to add one or more of the colour_description
elements, then the colour_description elements the user did not explicitly
request to be set are set to zero and not to the value equal to
unknown/unspecified (namely 2). A value of zero is not only inappropriate,
but explicitly forbidden. This is fixed by inferring the right default
values during the reading process if the elements are absent; moreover,
changing any of the colour_description elements to zero is now no longer
permitted.

Furthermore, if a sequence display extension has to be added, the
earlier code set some fields to their default value twice. This has been
changed, too.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt at gmail.com>
---
 libavcodec/cbs_mpeg2.c                 | 15 +++++++++++++++
 libavcodec/cbs_mpeg2_syntax_template.c |  4 ++++
 libavcodec/mpeg2_metadata_bsf.c        | 18 ++++++++++++------
 3 files changed, 31 insertions(+), 6 deletions(-)

diff --git a/libavcodec/cbs_mpeg2.c b/libavcodec/cbs_mpeg2.c
index 1d319e0947..437eac88a3 100644
--- a/libavcodec/cbs_mpeg2.c
+++ b/libavcodec/cbs_mpeg2.c
@@ -71,6 +71,10 @@
     (get_bits_left(rw) >= width && \
      (var = show_bits(rw, width)) == (compare))
 
+#define infer(name, value) do { \
+        current->name = value; \
+    } while (0)
+
 #include "cbs_mpeg2_syntax_template.c"
 
 #undef READ
@@ -79,6 +83,7 @@
 #undef xui
 #undef marker_bit
 #undef nextbits
+#undef infer
 
 
 #define WRITE
@@ -97,6 +102,15 @@
 
 #define nextbits(width, compare, var) (var)
 
+#define infer(name, value) do { \
+        if (current->name != (value)) { \
+            av_log(ctx->log_ctx, AV_LOG_WARNING, "Warning: " \
+                   "%s does not match inferred value: " \
+                   "%"PRId64", but should be %"PRId64".\n", \
+                   #name, (int64_t)current->name, (int64_t)(value)); \
+        } \
+    } while (0)
+
 #include "cbs_mpeg2_syntax_template.c"
 
 #undef READ
@@ -105,6 +119,7 @@
 #undef xui
 #undef marker_bit
 #undef nextbits
+#undef infer
 
 
 static void cbs_mpeg2_free_user_data(void *unit, uint8_t *content)
diff --git a/libavcodec/cbs_mpeg2_syntax_template.c b/libavcodec/cbs_mpeg2_syntax_template.c
index b9d53682fe..87db0ad039 100644
--- a/libavcodec/cbs_mpeg2_syntax_template.c
+++ b/libavcodec/cbs_mpeg2_syntax_template.c
@@ -144,6 +144,10 @@ static int FUNC(sequence_display_extension)(CodedBitstreamContext *ctx, RWContex
         uir(8, transfer_characteristics);
         uir(8, matrix_coefficients);
 #endif
+    } else {
+        infer(colour_primaries,         2);
+        infer(transfer_characteristics, 2);
+        infer(matrix_coefficients,      2);
     }
 
     ui(14, display_horizontal_size);
diff --git a/libavcodec/mpeg2_metadata_bsf.c b/libavcodec/mpeg2_metadata_bsf.c
index ba3a74afda..5aed41a008 100644
--- a/libavcodec/mpeg2_metadata_bsf.c
+++ b/libavcodec/mpeg2_metadata_bsf.c
@@ -147,18 +147,12 @@ static int mpeg2_metadata_update_fragment(AVBSFContext *bsf,
 
             if (ctx->colour_primaries >= 0)
                 sde->colour_primaries = ctx->colour_primaries;
-            else if (add_sde)
-                sde->colour_primaries = 2;
 
             if (ctx->transfer_characteristics >= 0)
                 sde->transfer_characteristics = ctx->transfer_characteristics;
-            else if (add_sde)
-                sde->transfer_characteristics = 2;
 
             if (ctx->matrix_coefficients >= 0)
                 sde->matrix_coefficients = ctx->matrix_coefficients;
-            else if (add_sde)
-                sde->matrix_coefficients = 2;
         }
     }
 
@@ -229,6 +223,18 @@ static int mpeg2_metadata_init(AVBSFContext *bsf)
     CodedBitstreamFragment *frag = &ctx->fragment;
     int err;
 
+#define VALIDITY_CHECK(name) do { \
+        if (!ctx->name) { \
+            av_log(bsf, AV_LOG_ERROR, "The value 0 for %s is " \
+                                      "forbidden.\n", #name); \
+            return AVERROR(EINVAL); \
+        } \
+    } while (0)
+    VALIDITY_CHECK(colour_primaries);
+    VALIDITY_CHECK(transfer_characteristics);
+    VALIDITY_CHECK(matrix_coefficients);
+#undef VALIDITY_CHECK
+
     err = ff_cbs_init(&ctx->cbc, AV_CODEC_ID_MPEG2VIDEO, bsf);
     if (err < 0)
         return err;
-- 
2.21.0