Mark Thompson:
> On 22/05/2019 02:04, 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.rheinha...@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
>
> Perhaps we could use the normal option checking to enforce this? Suppose we
> change the range from [-1, 255] to [0, 255] and make the do-nothing default
> value 0. Then the checks above become ctx->colour_primaries > 0 and this
> separate test is not needed.
>
There are two reasons why I didn't do this:
1. A user with only a background in (say) H.264 or H.265 might want to
put a value of 0 in there, thinking it is a legel value. Said user is
going to be surprised.
2. I have not given up hope on updating the AVCodecParameters (do you
remember
https://ffmpeg.org/pipermail/ffmpeg-devel/2018-December/236990.html ?)
and if 0 means do nothing, then it is not in line with the rest of cbs
and needs special handling there.
But both reasons are very weak and so I will consider your suggestion.
>> +
>> err = ff_cbs_init(&ctx->cbc, AV_CODEC_ID_MPEG2VIDEO, bsf);
>> if (err < 0)
>> return err;
>>
>
> - Mark
> _______________________________________________
> ffmpeg-devel mailing list
> ffmpeg-devel@ffmpeg.org
> https://ffmpeg.org/mailman/listinfo/ffmpeg-devel
>
> To unsubscribe, visit link above, or email
> ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
>
_______________________________________________
ffmpeg-devel mailing list
ffmpeg-devel@ffmpeg.org
https://ffmpeg.org/mailman/listinfo/ffmpeg-devel
To unsubscribe, visit link above, or email
ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
