[FFmpeg-devel] [PATCH v3 2/2] avcodec/dovi - correctly read el_bit_depth_minus8 and ext_mapping_idc

[James Almer]

On 5/22/2024 12:50 PM, Cosmin Stejerean via ffmpeg-devel wrote:
> From: Cosmin Stejerean <cosmin at cosmin.at>
> 
> These two fields are coded together into a single 16 bit integer with upper 8
> bits for ext_mapping_idc and lower 8 bits for el_bit_depth_minus8.
> 
> Furthermore ext_mapping_idc has two components, upper 3 bits and lower 5 bits.
> ---
>   libavcodec/dovi_rpudec.c | 7 ++++++-
>   libavcodec/dovi_rpuenc.c | 4 +++-
>   2 files changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/libavcodec/dovi_rpudec.c b/libavcodec/dovi_rpudec.c
> index 7c7eda9d09..af41ab5827 100644
> --- a/libavcodec/dovi_rpudec.c
> +++ b/libavcodec/dovi_rpudec.c
> @@ -411,13 +411,18 @@ int ff_dovi_rpu_parse(DOVIContext *s, const uint8_t *rpu, size_t rpu_size,
>   
>           if ((hdr->rpu_format & 0x700) == 0) {
>               int bl_bit_depth_minus8 = get_ue_golomb_31(gb);
> -            int el_bit_depth_minus8 = get_ue_golomb_31(gb);
> +            int el_bit_depth_minus8_and_ext_mapping_idc = get_ue_golomb_long(gb);
> +            int el_bit_depth_minus8 = el_bit_depth_minus8_and_ext_mapping_idc & 0xFF; // lowest 8 bits
> +            int ext_mapping_idc = (el_bit_depth_minus8_and_ext_mapping_idc & 0xFF00) >> 8; // upper 8 bits

nit: we usually do (foo >> 8) & 0xFF.

Also, coding two (maybe three) values in a single golomb code is evil.

> +
>               int vdr_bit_depth_minus8 = get_ue_golomb_31(gb);
>               VALIDATE(bl_bit_depth_minus8, 0, 8);
>               VALIDATE(el_bit_depth_minus8, 0, 8);
>               VALIDATE(vdr_bit_depth_minus8, 0, 8);
>               hdr->bl_bit_depth = bl_bit_depth_minus8 + 8;
>               hdr->el_bit_depth = el_bit_depth_minus8 + 8;
> +            hdr->ext_mapping_idc_0_4 = ext_mapping_idc & 0x1F; // lowest 5 bits of ext_mapping_idc
> +            hdr->ext_mapping_idc_5_7 = (ext_mapping_idc & 0xE0) >> 5; // upper 3 bits of ext_mapping_idc

Ditto.

>               hdr->vdr_bit_depth = vdr_bit_depth_minus8 + 8;
>               hdr->spatial_resampling_filter_flag = get_bits1(gb);
>               skip_bits(gb, 3); /* reserved_zero_3bits */
> diff --git a/libavcodec/dovi_rpuenc.c b/libavcodec/dovi_rpuenc.c
> index 3c3e0f84c0..91c0a85050 100644
> --- a/libavcodec/dovi_rpuenc.c
> +++ b/libavcodec/dovi_rpuenc.c
> @@ -444,6 +444,7 @@ int ff_dovi_rpu_generate(DOVIContext *s, const AVDOVIMetadata *metadata,
>       int vdr_dm_metadata_changed, vdr_rpu_id, use_prev_vdr_rpu, profile,
>           buffer_size, rpu_size, pad, zero_run;
>       int num_ext_blocks_v1, num_ext_blocks_v2;
> +    uint8_t ext_mapping_idc;
>       uint32_t crc;
>       uint8_t *dst;
>       if (!metadata) {
> @@ -551,7 +552,8 @@ int ff_dovi_rpu_generate(DOVIContext *s, const AVDOVIMetadata *metadata,
>       put_bits(pb, 1, hdr->bl_video_full_range_flag);
>       if ((hdr->rpu_format & 0x700) == 0) {
>           set_ue_golomb(pb, hdr->bl_bit_depth - 8);
> -        set_ue_golomb(pb, hdr->el_bit_depth - 8);
> +        ext_mapping_idc = (hdr->ext_mapping_idc_5_7 << 5) | hdr->ext_mapping_idc_0_4;
> +        set_ue_golomb(pb, (ext_mapping_idc << 8) | hdr->el_bit_depth - 8);
>           set_ue_golomb(pb, hdr->vdr_bit_depth - 8);
>           put_bits(pb, 1, hdr->spatial_resampling_filter_flag);
>           put_bits(pb, 3, 0); /* reserved_zero_3bits */