Re: [Patch v7 12/12] Documention: v4l: Documentation for HEVC CIDs

[Smitha T Murthy]

On Mon, 2018-01-29 at 14:27 +0100, Hans Verkuil wrote:
> On 01/29/2018 01:42 PM, Smitha T Murthy wrote:
> > On Wed, 2018-01-24 at 15:16 +0100, Hans Verkuil wrote:
> >> On 24/01/18 11:59, Smitha T Murthy wrote:
> >>> Added V4l2 controls for HEVC encoder
> >>>
> >>> Signed-off-by: Smitha T Murthy <smitha.t@xxxxxxxxxxx>
> >>> ---
> >>>  Documentation/media/uapi/v4l/extended-controls.rst | 400 +++++++++++++++++++++
> >>>  1 file changed, 400 insertions(+)
> >>>
> >>> diff --git a/Documentation/media/uapi/v4l/extended-controls.rst b/Documentation/media/uapi/v4l/extended-controls.rst
> >>> index dfe49ae..46ee2bf 100644
> >>> --- a/Documentation/media/uapi/v4l/extended-controls.rst
> >>> +++ b/Documentation/media/uapi/v4l/extended-controls.rst
> >>> @@ -1960,6 +1960,406 @@ enum v4l2_vp8_golden_frame_sel -
> >>>      1, 2 and 3 corresponding to encoder profiles 0, 1, 2 and 3.
> >>>  
> >>>  
> >>> +High Efficiency Video Coding (HEVC/H.265) Control Reference
> >>> +-----------------------------------------------------------
> >>> +
> >>> +The HEVC/H.265 controls include controls for encoding parameters of HEVC/H.265
> >>> +video codec.
> >>> +
> >>> +
> >>> +.. _hevc-control-id:
> >>> +
> >>> +HEVC/H.265 Control IDs
> >>> +^^^^^^^^^^^^^^^^^^^^^^
> >>> +
> >>> +``V4L2_CID_MPEG_VIDEO_HEVC_MIN_QP (integer)``
> >>> +    Minimum quantization parameter for HEVC.
> >>> +    Valid range: from 0 to 51.
> >>> +
> >>> +``V4L2_CID_MPEG_VIDEO_HEVC_MAX_QP (integer)``
> >>> +    Maximum quantization parameter for HEVC.
> >>> +    Valid range: from 0 to 51.
> >>
> >> You probably should mention the default values for MIN_QP and MAX_QP
> >> (I assume those are 0 and 51 and are not driver specific).
> >>
> > Yes these values are not driver specific.
> > I followed the way MAX_QP and MIN_QP are defined for other codecs like
> > H264, H263, MPEG4 where only valid range is mentioned.
> > 
> >>> +
> >>> +``V4L2_CID_MPEG_VIDEO_HEVC_I_FRAME_QP (integer)``
> >>> +    Quantization parameter for an I frame for HEVC.
> >>> +    Valid range: from 0 to 51.
> >>> +
> >>> +``V4L2_CID_MPEG_VIDEO_HEVC_P_FRAME_QP (integer)``
> >>> +    Quantization parameter for a P frame for HEVC.
> >>> +    Valid range: from 0 to 51.
> >>> +
> >>> +``V4L2_CID_MPEG_VIDEO_HEVC_B_FRAME_QP (integer)``
> >>> +    Quantization parameter for a B frame for HEVC.
> >>> +    Valid range: from 0 to 51.
> >>
> >> Sorry, this still isn't clear to me.
> >>
> >> If I set V4L2_CID_MPEG_VIDEO_HEVC_MAX_QP to 50, can I then still set
> >> V4L2_CID_MPEG_VIDEO_HEVC_B_FRAME_QP to 51? Or is 50 then the maximum?
> >>
> >> In other words, what is the relationship between these three controls
> >> and the MIN_QP/MAX_QP controls.
> >>
> > If we set V4L2_CID_MPEG_VIDEO_HEVC_MAX_QP as 50 then
> > V4L2_CID_MPEG_VIDEO_HEVC_B_FRAME_QP or
> > 4L2_CID_MPEG_VIDEO_HEVC_I_FRAME_QP or
> > V4L2_CID_MPEG_VIDEO_HEVC_P_FRAME_QP will have maximum as 50.
> > Similarly for minimum as well, the above three controls will adhere to
> > the V4L2_CID_MPEG_VIDEO_HEVC_MIN_QP set.
> > These controls have similar in relation as seen with
> > V4L2_CID_MPEG_VIDEO_H264_P_FRAME_QP and V4L2_CID_MPEG_VIDEO_H264_MAX_QP 
> > 
> >>> +
> >>> +``V4L2_CID_MPEG_VIDEO_HEVC_HIER_QP (boolean)``
> >>> +    HIERARCHICAL_QP allows the host to specify the quantization parameter
> >>> +    values for each temporal layer through HIERARCHICAL_QP_LAYER. This is
> >>> +    valid only if HIERARCHICAL_CODING_LAYER is greater than 1. Setting the
> >>> +    control value to 1 enables setting of the QP values for the layers.
> >>> +
> >>> +.. _v4l2-hevc-hier-coding-type:
> >>> +
> >>> +``V4L2_CID_MPEG_VIDEO_HEVC_HIER_CODING_TYPE``
> >>> +    (enum)
> >>> +
> >>> +enum v4l2_mpeg_video_hevc_hier_coding_type -
> >>> +    Selects the hierarchical coding type for encoding. Possible values are:
> >>> +
> >>> +.. raw:: latex
> >>> +
> >>> +    \begin{adjustbox}{width=\columnwidth}
> >>> +
> >>> +.. tabularcolumns:: |p{11.0cm}|p{10.0cm}|
> >>> +
> >>> +.. flat-table::
> >>> +    :header-rows:  0
> >>> +    :stub-columns: 0
> >>> +
> >>> +    * - ``V4L2_MPEG_VIDEO_HEVC_HIERARCHICAL_CODING_B``
> >>> +      - Use the B frame for hierarchical coding.
> >>> +    * - ``V4L2_MPEG_VIDEO_HEVC_HIERARCHICAL_CODING_P``
> >>> +      - Use the P frame for hierarchical coding.
> >>> +
> >>> +.. raw:: latex
> >>> +
> >>> +    \end{adjustbox}
> >>> +
> >>> +
> >>> +``V4L2_CID_MPEG_VIDEO_HEVC_HIER_CODING_LAYER (integer)``
> >>> +    Selects the hierarchical coding layer. In normal encoding
> >>> +    (non-hierarchial coding), it should be zero. Possible values are [0, 6].
> >>> +    0 indicates HIERARCHICAL CODING LAYER 0, 1 indicates HIERARCHICAL CODING
> >>> +    LAYER 1 and so on.
> >>> +
> >>> +``V4L2_CID_MPEG_VIDEO_HEVC_HIER_CODING_L0_QP (integer)``
> >>> +    Indicates quantization parameter for hierarchical coding layer 0.
> >>> +    For HEVC it can have a value of 0-51.
> >>> +
> >>> +``V4L2_CID_MPEG_VIDEO_HEVC_HIER_CODING_L1_QP (integer)``
> >>> +    Indicates quantization parameter for hierarchical coding layer 1.
> >>> +    For HEVC it can have a value of 0-51.
> >>> +
> >>> +``V4L2_CID_MPEG_VIDEO_HEVC_HIER_CODING_L2_QP (integer)``
> >>> +    Indicates quantization parameter for hierarchical coding layer 2.
> >>> +    For HEVC it can have a value of 0-51.
> >>> +
> >>> +``V4L2_CID_MPEG_VIDEO_HEVC_HIER_CODING_L3_QP (integer)``
> >>> +    Indicates quantization parameter for hierarchical coding layer 3.
> >>> +    For HEVC it can have a value of 0-51.
> >>> +
> >>> +``V4L2_CID_MPEG_VIDEO_HEVC_HIER_CODING_L4_QP (integer)``
> >>> +    Indicates quantization parameter for hierarchical coding layer 4.
> >>> +    For HEVC it can have a value of 0-51.
> >>> +
> >>> +``V4L2_CID_MPEG_VIDEO_HEVC_HIER_CODING_L5_QP (integer)``
> >>> +    Indicates quantization parameter for hierarchical coding layer 5.
> >>> +    For HEVC it can have a value of 0-51.
> >>> +
> >>> +``V4L2_CID_MPEG_VIDEO_HEVC_HIER_CODING_L6_QP (integer)``
> >>> +    Indicates quantization parameter for hierarchical coding layer 6.
> >>> +    For HEVC it can have a value of 0-51.
> >>
> >> Same here: how does MIN_QP/MAX_QP influence these controls, if at all.
> >>
> >> Regards,
> >>
> >> 	Hans
> >>
> >>
> > The values set in V4L2_CID_MPEG_VIDEO_HEVC_MIN_QP and
> > V4L2_CID_MPEG_VIDEO_HEVC_MAX_QP will give the limits for the L0-L6 QP
> > values that can be set.
> 
> OK. If you can clarify this in the documentation, then I can Ack this.
> 
> Note: if userspace changes MIN_QP or MAX_QP, then the driver should call
> v4l2_ctrl_modify_range() to update the ranges of the controls that are
> impacted by QP range changes. I'm not sure if that's done at the moment.
> 
> Regards,
> 
> 	Hans
> 
>