Re: [PATCH 1/2] media: v4l2-ctrls: add encoder maximum bitrate control

[Sachin Kumar Garg]

On 2/14/2026 12:59 AM, Nicolas Dufresne wrote:
> Le vendredi 13 février 2026 à 11:34 +0530, Sachin Kumar Garg a écrit :
> > Introduce V4L2_MPEG_VIDEO_BITRATE_MODE_MBR rate control for Encoder.
> > Encoder will choose appropriate quantization parameter and do the
> > smart bit allocation to set the frame maximum bitrate level as per
> > the Bitrate value configured.
> >
> > Signed-off-by: Sachin Kumar Garg <sachin.garg@xxxxxxxxxxxxxxxx>
> > ---
> >   Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst | 7 +++++++
> >   drivers/media/v4l2-core/v4l2-ctrls-defs.c                 | 1 +
> >   include/uapi/linux/v4l2-controls.h                        | 1 +
> >   3 files changed, 9 insertions(+)
> >
> > diff --git a/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
> > b/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
> > index c8890cb5e00a..6b2dfabfc4fd 100644
> > --- a/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
> > +++ b/Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
> > @@ -577,6 +577,13 @@ enum v4l2_mpeg_video_bitrate_mode -
> >         - Constant bitrate
> >       * - ``V4L2_MPEG_VIDEO_BITRATE_MODE_CQ``
> >         - Constant quality
> > +    * - ``V4L2_MPEG_VIDEO_BITRATE_MODE_MBR``
> > +      MBR Rate Control is a VBR Rate Control mode optimized for
> > +      surveillance video contents which has high temporal correlation
> > +      due to static camera positions. This Rate Control smartly identifies
> > +      key-frames in the scene, and allocates more bits to them to improve
> > +      the coding efficiency by taking advantage of high temporal
> > +      correlation in surveillance videos.
>
> This is a bit vague, and it sounds like how you'd describe a proprietary thing.
> Are you sure this is a generic mode that other vendors will support ? If not,
> perhaps it should be visible in the API ?
>
> Nicolas

Hi Nicolas, sorry for the late reply — we were aligning internally on 
the exact behavior and naming. This is Qualcomm defined Rate control. 
This is mainly useful for very low bitrate / high temporal-correlation 
content (e.g., static camera).
If the consensus is that this is not generic enough across vendors, we 
can instead expose it as a driver-specific control rather than a new 
global V4L2 bitrate mode.

Thanks,
Sachin

> >   
> >   
> >   
> > diff --git a/drivers/media/v4l2-core/v4l2-ctrls-defs.c b/drivers/media/v4l2-
> > core/v4l2-ctrls-defs.c
> > index 551426c4cd01..b336171539a7 100644
> > --- a/drivers/media/v4l2-core/v4l2-ctrls-defs.c
> > +++ b/drivers/media/v4l2-core/v4l2-ctrls-defs.c
> > @@ -154,6 +154,7 @@ const char * const *v4l2_ctrl_get_menu(u32 id)
> >   		"Variable Bitrate",
> >   		"Constant Bitrate",
> >   		"Constant Quality",
> > +		"Maximum Bitrate",
> >   		NULL
> >   	};
> >   	static const char * const mpeg_stream_type[] = {
> > diff --git a/include/uapi/linux/v4l2-controls.h b/include/uapi/linux/v4l2-
> > controls.h
> > index 68dd0c4e47b2..614fc2c4c81d 100644
> > --- a/include/uapi/linux/v4l2-controls.h
> > +++ b/include/uapi/linux/v4l2-controls.h
> > @@ -412,6 +412,7 @@ enum v4l2_mpeg_video_bitrate_mode {
> >   	V4L2_MPEG_VIDEO_BITRATE_MODE_VBR = 0,
> >   	V4L2_MPEG_VIDEO_BITRATE_MODE_CBR = 1,
> >   	V4L2_MPEG_VIDEO_BITRATE_MODE_CQ  = 2,
> > +	V4L2_MPEG_VIDEO_BITRATE_MODE_MBR = 3,
> >   };
> >   #define V4L2_CID_MPEG_VIDEO_BITRATE		(V4L2_CID_CODEC_BASE+207)
> >   #define V4L2_CID_MPEG_VIDEO_BITRATE_PEAK	(V4L2_CID_CODEC_BASE+208)