linux-kernel - Re: [PATCH v4 1/5] media: uapi: videodev2: Add support for AV1 stateful decoder

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Message-ID: <47a16514-9cc1-46c9-b0d8-029c5bc44638@oss.qualcomm.com>
Date: Fri, 7 Nov 2025 20:29:34 -0800
From: Deepa Guthyappa Madivalara <deepa.madivalara@....qualcomm.com>
To: Nicolas Dufresne <nicolas.dufresne@...labora.com>,
        Hans Verkuil <hverkuil+cisco@...nel.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Vikash Garodia <vikash.garodia@....qualcomm.com>,
        Dikshita Agarwal <dikshita.agarwal@....qualcomm.com>,
        Abhinav Kumar <abhinav.kumar@...ux.dev>,
        Bryan O'Donoghue <bod@...nel.org>
Cc: linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, kernel test robot <lkp@...el.com>,
        Bryan O'Donoghue <bryan.odonoghue@...aro.org>
Subject: Re: [PATCH v4 1/5] media: uapi: videodev2: Add support for AV1
 stateful decoder


On 11/7/2025 5:41 AM, Nicolas Dufresne wrote:
> Le vendredi 07 novembre 2025 à 10:25 +0100, Hans Verkuil a écrit :
>> On 03/11/2025 14:24, Deepa Guthyappa Madivalara wrote:
>>> Introduce a new pixel format, V4L2_PIX_FMT_AV1, to the
>>> Video4Linux2(V4L2) API. This format is intended for AV1
>>> bitstreams in stateful decoding/encoding workflows.
>>> The fourcc code 'AV10' is used to distinguish
>>> this format from the existing V4L2_PIX_FMT_AV1_FRAME,
>>> which is used for stateless AV1 decoder implementation.
>>>
>>> Reviewed-by: Bryan O'Donoghue <bryan.odonoghue@...aro.org>
>>> Reviewed-by: Nicolas Dufresne <nicolas.dufresne@...labora.com>
>>> Signed-off-by: Deepa Guthyappa Madivalara <deepa.madivalara@....qualcomm.com>
>>> ---
>>>   Documentation/userspace-api/media/v4l/pixfmt-compressed.rst | 8 ++++++++
>>>   include/uapi/linux/videodev2.h                              | 1 +
>>>   2 files changed, 9 insertions(+)
>>>
>>> diff --git a/Documentation/userspace-api/media/v4l/pixfmt-compressed.rst b/Documentation/userspace-api/media/v4l/pixfmt-compressed.rst
>>> index c7efb0465db6480fe35be8557728c196e0e530f4..0c70410ffd4d58e0719d3cf13ad336c97b454ae9 100644
>>> --- a/Documentation/userspace-api/media/v4l/pixfmt-compressed.rst
>>> +++ b/Documentation/userspace-api/media/v4l/pixfmt-compressed.rst
>>> @@ -275,6 +275,14 @@ Compressed Formats
>>>           of macroblocks to decode a full corresponding frame to the matching
>>>           capture buffer.
>>>   
>>> +    * .. _V4L2-PIX-FMT-AV1:
>>> +
>>> +      - ``V4L2_PIX_FMT_AV1``
>>> +      - 'AV01'
>>> +      - AV1 compressed video frame. This format is adapted for implementing AV1
>>> +        pipeline. The decoder implements stateful video decoder and expects one
>>> +        Temporal Unit per buffer from OBU-stream or AnnexB.
>> OK, but the next patch says:
>>
>> 		case V4L2_PIX_FMT_AV1:		descr = "AV1 OBU stream"; break;
>>
>> And Nicolas said here:
> Hmm, good catch, we had quite a bit of back and forth actually on the subject.
> The discussion went toward that this is OBU Stream format, but it is conceivable
> to enable Annex B support in the future using a control. That mandates that OBU
> stream must always be supported for that format.

Thanks for the comments. I had a similar understanding as Nicolas.
To keep things clear updated v4 to just have OBU Stream.
Thanks,
Deepa

> I'd drop the "or AnnexB". Then I'd try and harmonize how we write OBU stream, I
> prefer without the -.
>
>> https://lore.kernel.org/linux-media/544147436308901fba85d6de48380c0c1eea7c67.camel@ndufresne.ca/
>>
>> "Perhaps "AV1 OBU stream", so its clear its no Annex B ?"
>>
>> So if this is just for OBU streams and not Annex B, then the description is wrong.
>>
>> Since I'm no AV1 expert and have no idea what the difference between OBU and Annex B streams is,
>> I can only comment on what looks like an inconsistency.
> Annex B is very unlike H.264 annex b. Its adds a wrapper around time units,
> making it faster to walk through displayable frames when you have the ability to
> skip bytes. I've only ever seen it in tests vectors so far. My impression is
> that we'll never have a hardware that requires that.
>
> Nicolas
>
>> Regards,
>>
>> 	Hans
>>
>>> +        The encoder generates one Temporal Unit per buffer.
>>>   .. raw:: latex
>>>   
>>>       \normalsize
>>> diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
>>> index becd08fdbddb857f8f2bf205d2164dc6e20e80b2..cf0b71bbe0f9d397e1e6c88433a0fc3ba11fb947 100644
>>> --- a/include/uapi/linux/videodev2.h
>>> +++ b/include/uapi/linux/videodev2.h
>>> @@ -775,6 +775,7 @@ struct v4l2_pix_format {
>>>   #define V4L2_PIX_FMT_H264_SLICE v4l2_fourcc('S', '2', '6', '4') /* H264 parsed slices */
>>>   #define V4L2_PIX_FMT_HEVC_SLICE v4l2_fourcc('S', '2', '6', '5') /* HEVC parsed slices */
>>>   #define V4L2_PIX_FMT_AV1_FRAME v4l2_fourcc('A', 'V', '1', 'F') /* AV1 parsed frame */
>>> +#define V4L2_PIX_FMT_AV1      v4l2_fourcc('A', 'V', '0', '1') /* AV1 */
>>>   #define V4L2_PIX_FMT_SPK      v4l2_fourcc('S', 'P', 'K', '0') /* Sorenson Spark */
>>>   #define V4L2_PIX_FMT_RV30     v4l2_fourcc('R', 'V', '3', '0') /* RealVideo 8 */
>>>   #define V4L2_PIX_FMT_RV40     v4l2_fourcc('R', 'V', '4', '0') /* RealVideo 9 & 10 */
>>>