[FFmpeg-devel] [PATCH 3/4] 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                 |  8 ++++++++
 libavcodec/cbs_mpeg2_syntax_template.c |  4 ++++
 libavcodec/mpeg2_metadata_bsf.c        | 18 ++++++++++++------
 3 files changed, 24 insertions(+), 6 deletions(-)

diff --git a/libavcodec/cbs_mpeg2.c b/libavcodec/cbs_mpeg2.c
index 066ea83970..954adc7d57 100644
--- a/libavcodec/cbs_mpeg2.c
+++ b/libavcodec/cbs_mpeg2.c
@@ -70,6 +70,10 @@
     (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
@@ -78,6 +82,7 @@
 #undef xuir
 #undef marker_bit
 #undef nextbits
+#undef infer
 
 
 #define WRITE
@@ -96,6 +101,8 @@
 
 #define nextbits(width, compare, var) (var)
 
+#define infer(name, value)
+
 #include "cbs_mpeg2_syntax_template.c"
 
 #undef READ
@@ -104,6 +111,7 @@
 #undef xuir
 #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 745a123649..7b3f225396 100644
--- a/libavcodec/cbs_mpeg2_syntax_template.c
+++ b/libavcodec/cbs_mpeg2_syntax_template.c
@@ -128,6 +128,10 @@ static int FUNC(sequence_display_extension)(CodedBitstreamContext *ctx, RWContex
         uir(8, colour_primaries,         1, 255);
         uir(8, transfer_characteristics, 1, 255);
         uir(8, matrix_coefficients,      1, 255);
+    } 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..bb69001cef 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