[FFmpeg-devel] [PATCH WIP 4/5] avcodec/hevc/sei: Add support for alpha channel information

[James Almer]

On 12/11/2024 1:23 AM, Zhao Zhili wrote:
> From: Zhao Zhili <zhilizhao at tencent.com>
> 
> ---
>   libavcodec/hevc/sei.c | 30 ++++++++++++++++++++++++++++++
>   libavcodec/hevc/sei.h | 14 ++++++++++++++
>   2 files changed, 44 insertions(+)
> 
> diff --git a/libavcodec/hevc/sei.c b/libavcodec/hevc/sei.c
> index e11a33773c..56983fe96e 100644
> --- a/libavcodec/hevc/sei.c
> +++ b/libavcodec/hevc/sei.c
> @@ -150,6 +150,34 @@ static int decode_nal_sei_timecode(HEVCSEITimeCode *s, GetBitContext *gb)
>       return 0;
>   }
>   
> +static int decode_nal_sei_alpha_info(HEVCSEIAlphaChannelInfo *s, GetBitContext *gb)
> +{
> +    int length;
> +
> +    s->has_alpha_channel_info = true;
> +
> +    s->alpha_channel_cancel_flag = get_bits1(gb);
> +    if (!s->alpha_channel_cancel_flag) {

This should trigger when alpha_channel_cancel_flag is 1.

> +        s->alpha_channel_use_idc = 2;
> +        s->alpha_channel_incr_flag = 0;
> +        s->alpha_channel_clip_flag = 0;
> +
> +        return 0;
> +    }
> +
> +    s->alpha_channel_use_idc = get_bits(gb, 3);
> +    s->alpha_channel_bit_depth_minus8 = get_bits(gb, 3);
> +    length = s->alpha_channel_bit_depth_minus8 + 9;
> +    s->alpha_transparent_value = get_bits(gb, length);
> +    s->alpha_opaque_value = get_bits(gb, length);
> +    s->alpha_channel_incr_flag = get_bits1(gb);
> +    s->alpha_channel_clip_flag = get_bits1(gb);
> +    if (s->alpha_channel_clip_flag)
> +        s->alpha_channel_clip_type_flag = get_bits1(gb);
> +
> +    return 0;
> +}
> +
>   static int decode_nal_sei_3d_reference_displays_info(HEVCSEITDRDI *s, GetBitContext *gb)
>   {
>       s->prec_ref_display_width = get_ue_golomb(gb);
> @@ -216,6 +244,8 @@ static int decode_nal_sei_prefix(GetBitContext *gb, GetByteContext *gbyte,
>           return decode_nal_sei_active_parameter_sets(s, gb, logctx);
>       case SEI_TYPE_TIME_CODE:
>           return decode_nal_sei_timecode(&s->timecode, gb);
> +    case SEI_TYPE_ALPHA_CHANNEL_INFO:
> +        return decode_nal_sei_alpha_info(&s->alpha, gb);
>       case SEI_TYPE_THREE_DIMENSIONAL_REFERENCE_DISPLAYS_INFO:
>           return decode_nal_sei_3d_reference_displays_info(&s->tdrdi, gb);
>       default: {
> diff --git a/libavcodec/hevc/sei.h b/libavcodec/hevc/sei.h
> index ee640003bc..54122c27df 100644
> --- a/libavcodec/hevc/sei.h
> +++ b/libavcodec/hevc/sei.h
> @@ -21,6 +21,7 @@
>   #ifndef AVCODEC_HEVC_SEI_H
>   #define AVCODEC_HEVC_SEI_H
>   
> +#include <stdbool.h>

Are we using bool anywhere else? Afaik, we just use uint8_t everywhere 
since it's going to be a whole byte anyway.

>   #include <stdint.h>
>   
>   #include "libavutil/buffer.h"
> @@ -95,6 +96,18 @@ typedef struct HEVCSEITDRDI {
>       uint8_t three_dimensional_reference_displays_extension_flag;
>   } HEVCSEITDRDI;
>   
> +typedef struct HEVCSEIAlphaChannelInfo {
> +    bool     has_alpha_channel_info;
> +    uint8_t  alpha_channel_cancel_flag;
> +    uint8_t  alpha_channel_use_idc;
> +    uint8_t  alpha_channel_bit_depth_minus8;
> +    uint16_t alpha_transparent_value;
> +    uint16_t alpha_opaque_value;
> +    uint8_t  alpha_channel_incr_flag;
> +    uint8_t  alpha_channel_clip_flag;
> +    uint8_t  alpha_channel_clip_type_flag;
> +} HEVCSEIAlphaChannelInfo;
> +
>   typedef struct HEVCSEI {
>       H2645SEI common;
>       HEVCSEIPictureHash picture_hash;
> @@ -102,6 +115,7 @@ typedef struct HEVCSEI {
>       int active_seq_parameter_set_id;
>       HEVCSEITimeCode timecode;
>       HEVCSEITDRDI tdrdi;
> +    HEVCSEIAlphaChannelInfo alpha;
>   } HEVCSEI;
>   
>   struct HEVCParamSets;

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