[FFmpeg-devel,3/4] mpeg2_metadata, cbs_mpeg2: Fix handling of colour_description

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@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(-)

On 4/21/2019 11:04 AM, Andreas Rheinhardt wrote:
> 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@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)

Shouldn't this one check that current->name == value, like in other modules?

> +
>  #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;
>