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

From: Paul Kocialkowski
Date: Fri Jan 25 2019 - 08:04:45 EST

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Hi,

On Thu, 2019-01-24 at 20:23 +0800, Ayaka wrote:
>
> Sent from my iPad
>
> > On Jan 24, 2019, at 6:27 PM, Paul Kocialkowski <paul.kocialkowski@xxxxxxxxxxx> wrote:
> >
> > Hi,
> >
> > > On Thu, 2019-01-10 at 21:32 +0800, ayaka wrote:
> > > I forget a important thing, for the rkvdec and rk hevc decoder, it would
> > > requests cabac table, scaling list, picture parameter set and reference
> > > picture storing in one or various of DMA buffers. I am not talking about
> > > the data been parsed, the decoder would requests a raw data.
> > >
> > > For the pps and rps, it is possible to reuse the slice header, just let
> > > the decoder know the offset from the bitstream bufer, I would suggest to
> > > add three properties(with sps) for them. But I think we need a method to
> > > mark a OUTPUT side buffer for those aux data.
> >
> > I'm quite confused about the hardware implementation then. From what
> > you're saying, it seems that it takes the raw bitstream elements rather
> > than parsed elements. Is it really a stateless implementation?
> >
> > The stateless implementation was designed with the idea that only the
> > raw slice data should be passed in bitstream form to the decoder. For
> > H.264, it seems that some decoders also need the slice header in raw
> > bitstream form (because they take the full slice NAL unit), see the
> > discussions in this thread:
> > media: docs-rst: Document m2m stateless video decoder interface
>
> Stateless just mean it wonât track the previous result, but I donât
> think you can define what a date the hardware would need. Even you
> just build a dpb for the decoder, it is still stateless, but parsing
> less or more data from the bitstream doesnât stop a decoder become a
> stateless decoder.

Yes fair enough, the format in which the hardware decoder takes the
bitstream parameters does not make it stateless or stateful per-se.
It's just that stateless decoders should have no particular reason for
parsing the bitstream on their own since the hardware can be designed
with registers for each relevant bitstream element to configure the
decoding pipeline. That's how GPU-based decoder implementations are
implemented (VAAPI/VDPAU/NVDEC, etc).

So the format we have agreed on so far for the stateless interface is
to pass parsed elements via v4l2 control structures.

If the hardware can only work by parsing the bitstream itself, I'm not
sure what the best solution would be. Reconstructing the bitstream in
the kernel is a pretty bad option, but so is parsing in the kernel or
having the data both in parsed and raw forms. Do you see another
possibility?

Cheers,

Paul

> > Can you detail exactly what the rockchip decoder absolutely needs in
> > raw bitstream format?
> >
> > Cheers,
> >
> > Paul
> >
> > > > On 1/8/19 6:00 PM, Ayaka wrote:
> > > > 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
> > > > >
> > --
> > Paul Kocialkowski, Bootlin
> > Embedded Linux and kernel engineering
> > https://bootlin.com
> >
--
Paul Kocialkowski, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com

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