Re: [FFmpeg-devel] [PATCH v1 14/19] avcodec/cbs_sei_syntax_template: add sei message frame_field_information

[Andreas Rheinhardt <andreas.rheinhardt@outlook.com>]

James Almer:
> On 4/25/2025 7:08 PM, Andreas Rheinhardt wrote:
>> toqsxw@gmail.com:
>>> From: Wu Jianhua <toqsxw@outlook.com>
>>>
>>> Signed-off-by: Wu Jianhua <toqsxw@outlook.com>
>>> ---
>>>   libavcodec/cbs_h2645.c               |  6 ++++++
>>>   libavcodec/cbs_sei.h                 | 12 ++++++++++++
>>>   libavcodec/cbs_sei_syntax_template.c | 26 ++++++++++++++++++++++++++
>>>   3 files changed, 44 insertions(+)
>>>
>>> diff --git a/libavcodec/cbs_h2645.c b/libavcodec/cbs_h2645.c
>>> index c868770209..6677134d77 100644
>>> --- a/libavcodec/cbs_h2645.c
>>> +++ b/libavcodec/cbs_h2645.c
>>> @@ -2199,6 +2199,12 @@ static const SEIMessageTypeDescriptor
>>> cbs_sei_common_types[] = {
>>>           sizeof(SEIRawDisplayOrientation),
>>>           SEI_MESSAGE_RW(sei, display_orientation)
>>>       },
>>> +    {
>>> +        SEI_TYPE_FRAME_FIELD_INFO,
>>> +        1, 0,
>>> +        sizeof(SEIRawFrameFieldInformation),
>>> +        SEI_MESSAGE_RW(sei, frame_field_information)
>>> +    },
>>>       SEI_MESSAGE_TYPE_END,
>>>   };
>>>   diff --git a/libavcodec/cbs_sei.h b/libavcodec/cbs_sei.h
>>> index 7be12e33e0..81867b79a7 100644
>>> --- a/libavcodec/cbs_sei.h
>>> +++ b/libavcodec/cbs_sei.h
>>> @@ -125,6 +125,18 @@ typedef struct SEIRawDisplayOrientation {
>>>       uint8_t      display_orientation_reserved_zero_3bits;
>>>   } SEIRawDisplayOrientation;
>>>   +typedef struct SEIRawFrameFieldInformation {
>>> +    uint8_t      ffi_field_pic_flag;
>>> +    uint8_t      ffi_bottom_field_flag;
>>> +    uint8_t      ffi_pairing_indicated_flag;
>>> +    uint8_t      ffi_paired_with_next_field_flag;
>>> +    uint8_t      ffi_display_fields_from_frame_flag;
>>> +    uint8_t      ffi_top_field_first_flag;
>>> +    uint8_t      ffi_display_elemental_periods_minus1;
>>> +    uint8_t      ffi_source_scan_type;
>>> +    uint8_t      ffi_duplicate_flag;
>>> +} SEIRawFrameFieldInformation;
>>> +
>>>   typedef struct SEIRawMessage {
>>>       uint32_t     payload_type;
>>>       uint32_t     payload_size;
>>> diff --git a/libavcodec/cbs_sei_syntax_template.c b/libavcodec/
>>> cbs_sei_syntax_template.c
>>> index fb19f6ee42..e6863a0fd7 100644
>>> --- a/libavcodec/cbs_sei_syntax_template.c
>>> +++ b/libavcodec/cbs_sei_syntax_template.c
>>> @@ -295,6 +295,32 @@ SEI_FUNC(display_orientation,
>>> (CodedBitstreamContext *ctx, RWContext *rw,
>>>       return 0;
>>>   }
>>>   +SEI_FUNC(frame_field_information, (CodedBitstreamContext *ctx,
>>> RWContext *rw,
>>> +                                       SEIRawFrameFieldInformation
>>> *current,
>>> +                                       SEIMessageState *state))
>>> +{
>>> +    int err;
>>> +
>>> +    HEADER("Frame-field information");
>>> +
>>> +    flag(ffi_field_pic_flag);
>>> +    if (current->ffi_field_pic_flag) {
>>> +        flag(ffi_bottom_field_flag);
>>> +        flag(ffi_pairing_indicated_flag);
>>> +        if (current->ffi_pairing_indicated_flag)
>>> +            flag(ffi_paired_with_next_field_flag);
>>> +    } else {
>>> +        flag(ffi_display_fields_from_frame_flag);
>>> +        if (current->ffi_display_fields_from_frame_flag)
>>> +            flag(ffi_top_field_first_flag);
>>> +        u(8, ffi_display_elemental_periods_minus1, 0, 0xff);
>>> +    }
>>> +    u(2, ffi_source_scan_type, 0, 3);
>>> +    flag(ffi_duplicate_flag);
>>> +
>>> +    return 0;
>>> +}
>>> +
>>>   static int FUNC(message)(CodedBitstreamContext *ctx, RWContext *rw,
>>>                            SEIRawMessage *current)
>>>   {
>>
>> This does really not seem like a common SEI, yet you add it to the
>> common ones.
> 
> It's in ITU-T H.274, which is what the common list contains. It's used
> as fallback if a SEI type is not a H.26x specific one.
> 

I know and this makes it wrong. It will e.g. be used for H.264 SEI type
168, although this SEI does not exist in H.264 (unless I am mistaken
about the last point, but I don't think I am).

- Andreas

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