Date:   Thu, 24 Jan 2019 20:19:12 +0800
From:   Ayaka <ayaka@...lik.info>
To:     Paul Kocialkowski <paul.kocialkowski@...tlin.com>
Cc:     Randy Li <randy.li@...k-chips.com>,
        Jernej Škrabec <jernej.skrabec@...il.com>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        devel@...verdev.osuosl.org, linux-arm-kernel@...ts.infradead.org,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Hans Verkuil <hverkuil@...all.nl>,
        Ezequiel Garcia <ezequiel@...labora.com>,
        Tomasz Figa <tfiga@...omium.org>,
        Alexandre Courbot <acourbot@...omium.org>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        linux-rockchip@...ts.infradead.org
Subject: Re: [linux-sunxi] [PATCH v2 1/2] media: v4l: Add definitions for the HEVC slice format and controls



Sent from my iPad

> On Jan 24, 2019, at 6:36 PM, Paul Kocialkowski <paul.kocialkowski@...tlin.com> wrote:
> 
> Hi,
> 
>> On Tue, 2019-01-08 at 18:00 +0800, Ayaka wrote:
>> 
>> Sent from my iPad
>> 
>>> On Jan 8, 2019, at 4:38 PM, Paul Kocialkowski <paul.kocialkowski@...tlin.com> 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@...tlin.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).
>>> 
>>> 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.
> 
> I'm not sure what you meant here, sorry.
As we talked in IRC, I am not sure the field coded picture is supported in HEVC.
And I don’t why there would be two pic order cnt, a picture can only be used a short term or  a long term reference at one picture decoding
> 
>>>>>> 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. 
> 
> Right, the driver will allocate chunks of memory for the decoding
> metadata used by the hardware decoder.
> 
> Well, I don't think V4L2 has any mechanism to expose this data for now
> and since it's very specific to the hardware implementation, I guess
> the interest in having that is generally pretty low.
> 
> That's maybe something that could be added later if someone wants to
> work on it, but I think we are better off keeping this metadata hidden
> by the driver for now.
I am writing a V4l2 driver for rockchip based on the previous vendor driver I sent to mail list. I think I would offer a better way to describe the meta after that. But it need both work in derives and userspace, it would cost some times.
> 
>>>>>>>>> +
>>>>>>>>> +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
>>> 
> -- 
> Paul Kocialkowski, Bootlin
> Embedded Linux and kernel engineering
> https://bootlin.com
> 

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