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

[James Almer <jamrial@gmail.com>]

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On 4/25/2025 7:55 PM, Andreas Rheinhardt wrote:
> 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).

Then maybe ff_cbs_sei_find_type() should not look at 
cbs_sei_common_types for H.264 and H.265, given that those don't 
reference H.274, unlike H.266 which does (while not defining any SEI 
type at all).


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