[FFmpeg-devel] [PATCH] avformat/apvdec: export color information

[Mark Thompson]

On 27/04/2025 18:53, James Almer wrote:
> apv_read_header() reads enough information that the generic demux code doesn't
> attempt to read a frame to fill missing fields in codecpar, so make sure it's
> set here.
> 
> Signed-off-by: James Almer <jamrial at gmail.com>
> ---
>  libavformat/apvdec.c | 32 +++++++++++++++++++++++++++++---
>  1 file changed, 29 insertions(+), 3 deletions(-)
> 
> diff --git a/libavformat/apvdec.c b/libavformat/apvdec.c
> index e1ac34b003..94d2ce9965 100644
> --- a/libavformat/apvdec.c
> +++ b/libavformat/apvdec.c
> @@ -39,6 +39,11 @@ typedef struct APVHeaderInfo {
>      uint8_t  chroma_format_idc;
>      uint8_t  bit_depth_minus8;
>  
> +    int      color_primaries;
> +    int      transfer_characteristics;
> +    int      matrix_coefficients;
> +    int      full_range_flag;
> +
>      enum AVPixelFormat pixel_format;
>  } APVHeaderInfo;
>  
> @@ -55,6 +60,8 @@ static int apv_extract_header_info(APVHeaderInfo *info,
>  {
>      int zero, byte, bit_depth_index;
>  
> +    memset(info, 0, sizeof(*info));
> +
>      info->pbu_type = bytestream2_get_byte(gbc);
>      info->group_id = bytestream2_get_be16(gbc);
>  
> @@ -107,10 +114,24 @@ static int apv_extract_header_info(APVHeaderInfo *info,
>      // Ignore capture_time_distance.
>      bytestream2_skip(gbc, 1);
>  
> -    zero = bytestream2_get_byte(gbc);
> -    if (zero != 0)
> +    // two reserved_zero_8bits
> +    if (bytestream2_get_be16(gbc) != 0)
>          return AVERROR_INVALIDDATA;
>  
> +    // color_description_present_flag
> +    if (bytestream2_peek_byte(gbc) >> 7) {
> +        // We can read 32 bits as tile info is guaranteed to be present after this.
> +        unsigned color_description = bytestream2_get_be32(gbc);
> +
> +        if (bytestream2_get_bytes_left(gbc) <= 0)
> +            return AVERROR_INVALIDDATA;
> +
> +        info->color_primaries          = (color_description >> 23) & 0xff;
> +        info->transfer_characteristics = (color_description >> 15) & 0xff;
> +        info->matrix_coefficients      = (color_description >>  7) & 0xff;

For these "unspecified" has value 2, which will need to be set somewhere in no-description case rather than zero-init.  (Matrix coefficients 0 means identity, i.e. RGB, which we definitely don't want.)

> +        info->full_range_flag          = (color_description >>  6) & 1;
> +    }
> +
>      return 1;
>  }
>  
> @@ -157,7 +178,7 @@ static int apv_read_header(AVFormatContext *s)
>      AVStream *st;
>      GetByteContext gbc;
>      APVHeaderInfo header;
> -    uint8_t buffer[28];
> +    uint8_t buffer[64];

Could be smaller, but doesn't really matter.

>      uint32_t au_size, signature, pbu_size;
>      int err, size;
>  
> @@ -201,6 +222,11 @@ static int apv_read_header(AVFormatContext *s)
>      st->codecpar->level      = header.level_idc;
>      st->codecpar->width      = header.frame_width;
>      st->codecpar->height     = header.frame_height;
> +    st->codecpar->color_primaries = header.color_primaries;
> +    st->codecpar->color_trc       = header.transfer_characteristics;
> +    st->codecpar->color_space     = header.matrix_coefficients;
> +    st->codecpar->color_range     = header.full_range_flag ? AVCOL_RANGE_JPEG
> +                                                           : AVCOL_RANGE_MPEG;

Suggest st->codecpar->chroma_location = AVCHROMA_LOC_TOPLEFT as well?

>  
>      st->avg_frame_rate = (AVRational){ 30, 1 };
>      avpriv_set_pts_info(st, 64, 1, 30);

Thanks,

- Mark