Re: [linux-sunxi] [PATCH v2 1/2] media: v4l: Add definitions for the HEVC slice format and controls

[Ayaka <ayaka@soulik.info>]

Sent from my iPad

> On Jan 7, 2019, at 5:57 PM, Paul Kocialkowski <paul.kocialkowski@bootlin.com> wrote:
> 
> Hi,
> 
>> On Mon, 2019-01-07 at 11:49 +0800, Randy Li wrote:
>>> On 12/12/18 8:51 PM, Paul Kocialkowski wrote:
>>> Hi,
>>> 
>>> On Wed, 2018-12-05 at 21:59 +0100, Jernej Škrabec wrote:
>>> 
>>>>> +
>>>>> +#define V4L2_HEVC_DPB_ENTRY_RPS_ST_CURR_BEFORE    0x01
>>>>> +#define V4L2_HEVC_DPB_ENTRY_RPS_ST_CURR_AFTER    0x02
>>>>> +#define V4L2_HEVC_DPB_ENTRY_RPS_LT_CURR        0x03
>>>>> +
>>>>> +#define V4L2_HEVC_DPB_ENTRIES_NUM_MAX        16
>>>>> +
>>>>> +struct v4l2_hevc_dpb_entry {
>>>>> +    __u32    buffer_tag;
>>>>> +    __u8    rps;
>>>>> +    __u8    field_pic;
>>>>> +    __u16    pic_order_cnt[2];
>>>>> +};
>> 
>> Please add a property for reference index, if that rps is not used for 
>> this, some device would request that(not the rockchip one). And 
>> Rockchip's VDPU1 and VDPU2 for AVC would request a similar property.
> 
> What exactly is that reference index? Is it a bitstream element or
> something deduced from the bitstream?
> 
picture order count(POC) for HEVC and frame_num in AVC. I think it is the number used in list0(P slice and B slice) and list1(B slice).
>> Adding another buffer_tag for referring the memory of the motion vectors 
>> for each frames. Or a better method is add a meta data to echo picture 
>> buffer,  since the picture output is just the same as the original, 
>> display won't care whether the motion vectors are written the button of 
>> picture or somewhere else.
> 
> The motion vectors are passed as part of the raw bitstream data, in the
> slices. Is there a case where the motion vectors are coded differently?
No, it is an additional cache for decoder, even FFmpeg having such data, I think allwinner must output it into somewhere.
> 
>>>>> +
>>>>> +struct v4l2_hevc_pred_weight_table {
>>>>> +    __u8    luma_log2_weight_denom;
>>>>> +    __s8    delta_chroma_log2_weight_denom;
>>>>> +
>>>>> +    __s8    delta_luma_weight_l0[V4L2_HEVC_DPB_ENTRIES_NUM_MAX];
>>>>> +    __s8    luma_offset_l0[V4L2_HEVC_DPB_ENTRIES_NUM_MAX];
>>>>> +    __s8    delta_chroma_weight_l0[V4L2_HEVC_DPB_ENTRIES_NUM_MAX][2];
>>>>> +    __s8    chroma_offset_l0[V4L2_HEVC_DPB_ENTRIES_NUM_MAX][2];
>>>>> +
>>>>> +    __s8    delta_luma_weight_l1[V4L2_HEVC_DPB_ENTRIES_NUM_MAX];
>>>>> +    __s8    luma_offset_l1[V4L2_HEVC_DPB_ENTRIES_NUM_MAX];
>>>>> +    __s8    delta_chroma_weight_l1[V4L2_HEVC_DPB_ENTRIES_NUM_MAX][2];
>>>>> +    __s8    chroma_offset_l1[V4L2_HEVC_DPB_ENTRIES_NUM_MAX][2];
>>>>> +};
>>>>> +
>> Those properties I think are not necessary are applying for the 
>> Rockchip's device, may not work for the others.
> 
> Yes, it's possible that some of the elements are not necessary for some
> decoders. What we want is to cover all the elements that might be
> required for a decoder.
I wonder whether allwinner need that, those sao flag usually ignored by decoder in design. But more is better than less, it is hard to extend a v4l2 structure  in the future, maybe a new HEVC profile would bring a new property, it is still too early for HEVC.
> 
>>>>> +struct v4l2_ctrl_hevc_slice_params {
>>>>> +    __u32    bit_size;
>>>>> +    __u32    data_bit_offset;
>>>>> +
>>>>> +    /* ISO/IEC 23008-2, ITU-T Rec. H.265: NAL unit header */
>>>>> +    __u8    nal_unit_type;
>>>>> +    __u8    nuh_temporal_id_plus1;
>>>>> +
>>>>> +    /* ISO/IEC 23008-2, ITU-T Rec. H.265: General slice segment header */
>>>>> +    __u8    slice_type;
>>>>> +    __u8    colour_plane_id;
>> ----------------------------------------------------------------------------
>>>>> +    __u16    slice_pic_order_cnt;
>>>>> +    __u8    slice_sao_luma_flag;
>>>>> +    __u8    slice_sao_chroma_flag;
>>>>> +    __u8    slice_temporal_mvp_enabled_flag;
>>>>> +    __u8    num_ref_idx_l0_active_minus1;
>>>>> +    __u8    num_ref_idx_l1_active_minus1;
>> Rockchip's decoder doesn't use this part.
>>>>> +    __u8    mvd_l1_zero_flag;
>>>>> +    __u8    cabac_init_flag;
>>>>> +    __u8    collocated_from_l0_flag;
>>>>> +    __u8    collocated_ref_idx;
>>>>> +    __u8    five_minus_max_num_merge_cand;
>>>>> +    __u8    use_integer_mv_flag;
>>>>> +    __s8    slice_qp_delta;
>>>>> +    __s8    slice_cb_qp_offset;
>>>>> +    __s8    slice_cr_qp_offset;
>>>>> +    __s8    slice_act_y_qp_offset;
>>>>> +    __s8    slice_act_cb_qp_offset;
>>>>> +    __s8    slice_act_cr_qp_offset;
>>>>> +    __u8    slice_deblocking_filter_disabled_flag;
>>>>> +    __s8    slice_beta_offset_div2;
>>>>> +    __s8    slice_tc_offset_div2;
>>>>> +    __u8    slice_loop_filter_across_slices_enabled_flag;
>>>>> +
>>>>> +    /* ISO/IEC 23008-2, ITU-T Rec. H.265: Picture timing SEI message */
>>>>> +    __u8    pic_struct;
>> I think the decoder doesn't care about this, it is used for display.
> 
> The purpose of this field is to indicate whether the current picture is
> a progressive frame or an interlaced field picture, which is useful for
> decoding.
> 
> At least our decoder has a register field to indicate frame/top
> field/bottom field, so we certainly need to keep the info around.
> Looking at the spec and the ffmpeg implementation, it looks like this
> flag of the bitstream is the usual way to report field coding.
It depends whether the decoder cares about scan type or more, I wonder prefer general_interlaced_source_flag for just scan type, it would be better than reading another SEL.
> 
> Cheers,
> 
> Paul
Randy “ayaka” LI
> 
>>>>> +
>>>>> +    /* ISO/IEC 23008-2, ITU-T Rec. H.265: General slice segment header */
>>>>> +    struct v4l2_hevc_dpb_entry dpb[V4L2_HEVC_DPB_ENTRIES_NUM_MAX];
>>>>> +    __u8    num_active_dpb_entries;
>>>>> +    __u8    ref_idx_l0[V4L2_HEVC_DPB_ENTRIES_NUM_MAX];
>>>>> +    __u8    ref_idx_l1[V4L2_HEVC_DPB_ENTRIES_NUM_MAX];
>>>>> +
>>>>> +    __u8    num_rps_poc_st_curr_before;
>>>>> +    __u8    num_rps_poc_st_curr_after;
>>>>> +    __u8    num_rps_poc_lt_curr;
>>>>> +
>>>>> +    /* ISO/IEC 23008-2, ITU-T Rec. H.265: Weighted prediction parameter */
>>>>> +    struct v4l2_hevc_pred_weight_table pred_weight_table;
>>>>> +};
>>>>> +
>>>>>  #endif
> -- 
> Paul Kocialkowski, Bootlin (formerly Free Electrons)
> Embedded Linux and kernel engineering
> https://bootlin.com
>