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

[Smitha T Murthy <smitha.t@samsung.com>]

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@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).
> 
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.

Regards,
Smitha