linux-kernel - Re: [PATCH] media: v4l-ctrl: add control for variable frame rate

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Date:   Thu, 28 Mar 2019 15:57:18 +0100
From:   Hans Verkuil <hverkuil-cisco@...all.nl>
To:     Fish Lin <linfish@...gle.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Philipp Zabel <p.zabel@...gutronix.de>
Cc:     Paul Kocialkowski <paul.kocialkowski@...tlin.com>,
        Keiichi Watanabe <keiichiw@...omium.org>,
        Will Deacon <will.deacon@....com>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Tomasz Figa <tfiga@...omium.org>,
        Smitha T Murthy <smitha.t@...sung.com>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: v4l-ctrl: add control for variable frame rate

On 3/20/19 4:10 AM, Fish Lin wrote:
> These flag are added
> * V4L2_CID_MPEG_VIDEO_VFR_ENABLE
> * V4L2_CID_MPEG_VIDEO_VFR_MIN_FRAMERATE
> One is to set variable frame rate enable or not, another is to control
> minimal frame rate that video encoder should keep per second.
> 
> Signed-off-by: Fish Lin <linfish@...gle.com>
> ---
>  Documentation/media/uapi/v4l/ext-ctrls-codec.rst | 9 +++++++++
>  drivers/media/v4l2-core/v4l2-ctrls.c             | 3 +++
>  include/uapi/linux/v4l2-controls.h               | 3 +++
>  3 files changed, 15 insertions(+)
> 
> diff --git a/Documentation/media/uapi/v4l/ext-ctrls-codec.rst b/Documentation/media/uapi/v4l/ext-ctrls-codec.rst
> index c97fb7923be5..4bc013d71b67 100644
> --- a/Documentation/media/uapi/v4l/ext-ctrls-codec.rst
> +++ b/Documentation/media/uapi/v4l/ext-ctrls-codec.rst
> @@ -620,7 +620,16 @@ enum v4l2_mpeg_video_bitrate_mode -
>      * - Bit 24:31
>        - Must be zero.
>  
> +.. _v4l2-mpeg-video-variable-framerate:
>  
> +``V4L2_CID_MPEG_VIDEO_VFR_ENABLE (boolean)``
> +    Set variable framerate enable or not. When enabled, video encoder is able
> +    to drop frames based on some mechanism, like frame similarity or bitrate
> +    control (default disable).
> +
> +``V4L2_CID_MPEG_VIDEO_VFR_MIN_FRAMERATE (integer)``
> +    Minimal kept frame per second when variable framerate is enabled (default
> +    is input framerate).

You don't really have a concept of frames per second when encoding. What you
are probably trying to say is something like: "don't drop more than one frame for
every X frames" or something like that.

Which codecs support this? A decoder needs to know that a frame is missing, right?

What's the use-case for this?

Sorry, just trying to understand this better.

Regards,

	Hans

>  
>  .. _v4l2-mpeg-video-dec-pts:
>  
> diff --git a/drivers/media/v4l2-core/v4l2-ctrls.c b/drivers/media/v4l2-core/v4l2-ctrls.c
> index b79d3bbd8350..566c6552c9a0 100644
> --- a/drivers/media/v4l2-core/v4l2-ctrls.c
> +++ b/drivers/media/v4l2-core/v4l2-ctrls.c
> @@ -786,6 +786,8 @@ const char *v4l2_ctrl_get_name(u32 id)
>  	case V4L2_CID_MPEG_VIDEO_MB_RC_ENABLE:			return "H264 MB Level Rate Control";
>  	case V4L2_CID_MPEG_VIDEO_HEADER_MODE:			return "Sequence Header Mode";
>  	case V4L2_CID_MPEG_VIDEO_MAX_REF_PIC:			return "Max Number of Reference Pics";
> +	case V4L2_CID_MPEG_VIDEO_VFR_ENABLE:			return "Variable Frame Rate Enable";
> +	case V4L2_CID_MPEG_VIDEO_VFR_MIN_FRAMERATE:		return "VFR Minimal Frame Rate";
>  	case V4L2_CID_MPEG_VIDEO_H263_I_FRAME_QP:		return "H263 I-Frame QP Value";
>  	case V4L2_CID_MPEG_VIDEO_H263_P_FRAME_QP:		return "H263 P-Frame QP Value";
>  	case V4L2_CID_MPEG_VIDEO_H263_B_FRAME_QP:		return "H263 B-Frame QP Value";
> @@ -1108,6 +1110,7 @@ void v4l2_ctrl_fill(u32 id, const char **name, enum v4l2_ctrl_type *type,
>  	case V4L2_CID_MPEG_VIDEO_DECODER_SLICE_INTERFACE:
>  	case V4L2_CID_MPEG_VIDEO_FRAME_RC_ENABLE:
>  	case V4L2_CID_MPEG_VIDEO_MB_RC_ENABLE:
> +	case V4L2_CID_MPEG_VIDEO_VFR_ENABLE:
>  	case V4L2_CID_MPEG_VIDEO_H264_8X8_TRANSFORM:
>  	case V4L2_CID_MPEG_VIDEO_H264_VUI_SAR_ENABLE:
>  	case V4L2_CID_MPEG_VIDEO_MPEG4_QPEL:
> diff --git a/include/uapi/linux/v4l2-controls.h b/include/uapi/linux/v4l2-controls.h
> index 06479f2fb3ae..f1bf52eb0152 100644
> --- a/include/uapi/linux/v4l2-controls.h
> +++ b/include/uapi/linux/v4l2-controls.h
> @@ -404,6 +404,9 @@ enum v4l2_mpeg_video_multi_slice_mode {
>  #define V4L2_CID_MPEG_VIDEO_MV_V_SEARCH_RANGE		(V4L2_CID_MPEG_BASE+228)
>  #define V4L2_CID_MPEG_VIDEO_FORCE_KEY_FRAME		(V4L2_CID_MPEG_BASE+229)
>  
> +#define V4L2_CID_MPEG_VIDEO_VFR_ENABLE (V4L2_CID_MPEG_BASE + 250)
> +#define V4L2_CID_MPEG_VIDEO_VFR_MIN_FRAMERATE (V4L2_CID_MPEG_BASE + 251)
> +
>  #define V4L2_CID_MPEG_VIDEO_H263_I_FRAME_QP		(V4L2_CID_MPEG_BASE+300)
>  #define V4L2_CID_MPEG_VIDEO_H263_P_FRAME_QP		(V4L2_CID_MPEG_BASE+301)
>  #define V4L2_CID_MPEG_VIDEO_H263_B_FRAME_QP		(V4L2_CID_MPEG_BASE+302)
>