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

[Hans Verkuil <hverkuil@xs4all.nl>]

On 24/01/18 11:59, Smitha T Murthy wrote:
> Added V4l2 controls for HEVC encoder
> 
> Signed-off-by: Smitha T Murthy <smitha.t@samsung.com>
> ---
>  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).

> +
> +``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.

> +
> +``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