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

[Ayaka]

Sent from my iPad

> On Jan 8, 2019, at 4:38 PM, Paul Kocialkowski <paul.kocialkowski@xxxxxxxxxxx> wrote:
> 
> Hi,
> 
>> On Tue, 2019-01-08 at 09:16 +0800, Ayaka wrote:
>> 
>> Sent from my iPad
>> 
>>> On Jan 7, 2019, at 5:57 PM, Paul Kocialkowski <paul.kocialkowski@xxxxxxxxxxx> 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 Åkrabec 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).
> 
> The picture order count is already the last field of the DPB entry
> structure. There is one for each field picture.
As we are not sure whether there is a field coded slice or CTU, I would hold this part and else about the field.
> 
>>>> 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.
> 
> Ah yes I see what you mean! This is handled internally by our driver
> and not exposed to userspace. I don't think it would be a good idea to
> expose this cache or request that userspace allocates it like a video
> buffer.
> 
No, usually the driver should allocate, as the user space have no idea on size of each devices.
But for advantage user, application can fix a broken picture with a proper data or analysis a object motion from that.
So I would suggest attaching this information to a picture buffer as a meta data. 
>>>>>>> +
>>>>>>> +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.
> 
> Yes this is used by our decoder. The idea is to have all the basic
> bitstream elements in the structures (even if some decoders don't use
> them all) and add others for extension as separate controls later.
> 
>>>>>>> +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.
> 
> Well we still need a way to indicate if the current data is top or
> bottom field for interlaced. I don't think that knowing that the whole
> video is interlaced would be precise enough.
> 
> Cheers,
> 
> Paul
> 
>>>>>>> +
>>>>>>> +    /* 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
>>> 
> -- 
> Paul Kocialkowski, Bootlin (formerly Free Electrons)
> Embedded Linux and kernel engineering
> https://bootlin.com
>