Re: [PATCH 1/2] media: uapi: add WebP VP8 frame flag

[Nicolas Dufresne]

Hi Hugues,

Le mercredi 11 septembre 2024 à 15:50 +0200, Hugues Fruchet a écrit :
> Add a flag indicating that VP8 bitstream is a WebP picture.

Sounds like there should be some code changes in GStreamer that you haven't
disclosed. Mind sharing how this new uAPI is used ? I would also expect this
commit message to give more insight on what is special about WebP that makes
this flag required.

I would also need some more API or documentation that explain how we can
differentiate a upstream decoder that is capable of WebP decoding from one that
does not. I wonder if it would not have been better to define a new format ?
That being said, I haven't looked at all in the specification and only rely on
your cover letter and patch series.

Nicolas

> 
> Signed-off-by: Hugues Fruchet <hugues.fruchet@xxxxxxxxxxx>
> ---
>  .../userspace-api/media/v4l/ext-ctrls-codec-stateless.rst      | 3 +++
>  include/uapi/linux/v4l2-controls.h                             | 1 +
>  2 files changed, 4 insertions(+)
> 
> diff --git a/Documentation/userspace-api/media/v4l/ext-ctrls-codec-stateless.rst b/Documentation/userspace-api/media/v4l/ext-ctrls-codec-stateless.rst
> index 0da635691fdc..bb08aacddc9c 100644
> --- a/Documentation/userspace-api/media/v4l/ext-ctrls-codec-stateless.rst
> +++ b/Documentation/userspace-api/media/v4l/ext-ctrls-codec-stateless.rst
> @@ -1062,6 +1062,9 @@ FWHT Flags
>      * - ``V4L2_VP8_FRAME_FLAG_SIGN_BIAS_ALT``
>        - 0x20
>        - Sign of motion vectors when the alt frame is referenced.
> +    * - ``V4L2_VP8_FRAME_FLAG_WEBP``
> +      - 0x40
> +      - Indicates that this frame is a WebP picture.
>  
>  .. c:type:: v4l2_vp8_entropy_coder_state
>  
> diff --git a/include/uapi/linux/v4l2-controls.h b/include/uapi/linux/v4l2-controls.h
> index 974fd254e573..e41b62f2cb2b 100644
> --- a/include/uapi/linux/v4l2-controls.h
> +++ b/include/uapi/linux/v4l2-controls.h
> @@ -1897,6 +1897,7 @@ struct v4l2_vp8_entropy_coder_state {
>  #define V4L2_VP8_FRAME_FLAG_MB_NO_SKIP_COEFF	0x08
>  #define V4L2_VP8_FRAME_FLAG_SIGN_BIAS_GOLDEN	0x10
>  #define V4L2_VP8_FRAME_FLAG_SIGN_BIAS_ALT	0x20
> +#define V4L2_VP8_FRAME_FLAG_WEBP		0x40
>  
>  #define V4L2_VP8_FRAME_IS_KEY_FRAME(hdr) \
>  	(!!((hdr)->flags & V4L2_VP8_FRAME_FLAG_KEY_FRAME))