[PATCH v2 1/3] media: uapi: add WebP uAPI

[Nicolas Dufresne]

Hi Hugues,

as you know, naming is hard and I had to think about this one a little, see my
comment below.

Le mercredi 20 novembre 2024 à 12:01 +0100, Hugues Fruchet a écrit :
> This patch adds the WebP picture decoding kernel uAPI.
> 
> This design is based on currently available VP8 API implementation and
> aims to support the development of WebP stateless video codecs
> on Linux.
> 
> Signed-off-by: Hugues Fruchet <hugues.fruchet at foss.st.com>
> ---
>  Documentation/userspace-api/media/v4l/biblio.rst  |  9 +++++++++
>  .../userspace-api/media/v4l/pixfmt-compressed.rst | 15 +++++++++++++++
>  drivers/media/v4l2-core/v4l2-ioctl.c              |  1 +
>  include/uapi/linux/videodev2.h                    |  1 +
>  4 files changed, 26 insertions(+)
> 
> diff --git a/Documentation/userspace-api/media/v4l/biblio.rst b/Documentation/userspace-api/media/v4l/biblio.rst
> index 35674eeae20d..df3e963fc54f 100644
> --- a/Documentation/userspace-api/media/v4l/biblio.rst
> +++ b/Documentation/userspace-api/media/v4l/biblio.rst
> @@ -447,3 +447,12 @@ AV1
>  :title:     AV1 Bitstream & Decoding Process Specification
>  
>  :author:    Peter de Rivaz, Argon Design Ltd, Jack Haughton, Argon Design Ltd
> +
> +.. _webp:
> +
> +WEBP
> +====
> +
> +:title:     WEBP picture Bitstream & Decoding Process Specification
> +
> +:author:    Google (https://developers.google.com/speed/webp)
> diff --git a/Documentation/userspace-api/media/v4l/pixfmt-compressed.rst b/Documentation/userspace-api/media/v4l/pixfmt-compressed.rst
> index 806ed73ac474..e664e70b0619 100644
> --- a/Documentation/userspace-api/media/v4l/pixfmt-compressed.rst
> +++ b/Documentation/userspace-api/media/v4l/pixfmt-compressed.rst
> @@ -169,6 +169,21 @@ Compressed Formats
>  	this pixel format. The output buffer must contain the appropriate number
>  	of macroblocks to decode a full corresponding frame to the matching
>  	capture buffer.
> +    * .. _V4L2-PIX-FMT-WEBP-FRAME:
> +
> +      - ``V4L2_PIX_FMT_WEBP_FRAME``
> +      - 'WEBP'
> +      - WEBP VP8 parsed frame, excluding WEBP RIFF header, keeping only the VP8
> +	bistream including the frame header, as extracted from the container.
> +	This format is adapted for stateless video decoders that implement a
> +	WEBP pipeline with the :ref:`stateless_decoder`.
> +	Metadata associated with the frame to decode is required to be passed
> +	through the ``V4L2_CID_STATELESS_VP8_FRAME`` control.
> +	See the :ref:`associated Codec Control IDs <v4l2-codec-stateless-vp8>`.
> +	Exactly one output and one capture buffer must be provided for use with
> +	this pixel format. The output buffer must contain the appropriate number
> +	of macroblocks to decode a full corresponding frame to the matching
> +	capture buffer.

So after reading more about it, I think we should avoid the usage of the WEBP
name, as WEBP is clearly a RIFF based container format and supports 2 totally
different codecs. I think we should instead call this
V4L2_PIX_FMT_VP8_INTRA_FRAME. We should still document that these are used by
WebP for lossy compression, so that  readers can correlate.

Some folks will still wonder why a separate format, and the I still hold that it
fits better for the case we have one driver, with one video node that can handle
both, since you can probe these by simply using VIDIOC_ENUM_FMT, its easily
discoverable without introducing a new control, etc.

regards,
Nicolas

>  
>      * .. _V4L2-PIX-FMT-VP9:
>  
> diff --git a/drivers/media/v4l2-core/v4l2-ioctl.c b/drivers/media/v4l2-core/v4l2-ioctl.c
> index 0304daa8471d..e2ff03d0d773 100644
> --- a/drivers/media/v4l2-core/v4l2-ioctl.c
> +++ b/drivers/media/v4l2-core/v4l2-ioctl.c
> @@ -1501,6 +1501,7 @@ static void v4l_fill_fmtdesc(struct v4l2_fmtdesc *fmt)
>  		case V4L2_PIX_FMT_VC1_ANNEX_L:	descr = "VC-1 (SMPTE 412M Annex L)"; break;
>  		case V4L2_PIX_FMT_VP8:		descr = "VP8"; break;
>  		case V4L2_PIX_FMT_VP8_FRAME:    descr = "VP8 Frame"; break;
> +		case V4L2_PIX_FMT_WEBP_FRAME:    descr = "WEBP VP8 Frame"; break;
>  		case V4L2_PIX_FMT_VP9:		descr = "VP9"; break;
>  		case V4L2_PIX_FMT_VP9_FRAME:    descr = "VP9 Frame"; break;
>  		case V4L2_PIX_FMT_HEVC:		descr = "HEVC"; break; /* aka H.265 */
> diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
> index e7c4dce39007..09fff269e852 100644
> --- a/include/uapi/linux/videodev2.h
> +++ b/include/uapi/linux/videodev2.h
> @@ -757,6 +757,7 @@ struct v4l2_pix_format {
>  #define V4L2_PIX_FMT_VC1_ANNEX_L v4l2_fourcc('V', 'C', '1', 'L') /* SMPTE 421M Annex L compliant stream */
>  #define V4L2_PIX_FMT_VP8      v4l2_fourcc('V', 'P', '8', '0') /* VP8 */
>  #define V4L2_PIX_FMT_VP8_FRAME v4l2_fourcc('V', 'P', '8', 'F') /* VP8 parsed frame */
> +#define V4L2_PIX_FMT_WEBP_FRAME v4l2_fourcc('W', 'B', 'P', 'F') /* WEBP VP8 parsed frame */
>  #define V4L2_PIX_FMT_VP9      v4l2_fourcc('V', 'P', '9', '0') /* VP9 */
>  #define V4L2_PIX_FMT_VP9_FRAME v4l2_fourcc('V', 'P', '9', 'F') /* VP9 parsed frame */
>  #define V4L2_PIX_FMT_HEVC     v4l2_fourcc('H', 'E', 'V', 'C') /* HEVC aka H.265 */