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

[Sachin Kumar Garg <sachin.garg@oss.qualcomm.com>]

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@oss.qualcomm.com>
>> ---
>>   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)