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

[Hugues FRUCHET]

Hi Nicolas,

Thanks for reviewing.

On 9/11/24 19:12, Nicolas Dufresne wrote:
> 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.


GStreamer changes here:
https://gitlab.freedesktop.org/gstreamer/gstreamer/-/commit/138ecfac54ce85b273a26ff6f0fefe3998f8d436?merge_request_iid=7505

Verisilicon datasheet is not explicit on why WebP must be signaled to 
hardware but WebP decoding fails if not.
Seems to me that such a simple addition on an already existing flag is 
something acceptable and preferable to the development of a new complete 
uAPI for WebP decoding.

> 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))

BR,
Hugues.