linux-kernel - Re: [RFC PATCH v2] media: docs-rst: Document m2m stateless video decoder interface

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Message-ID: <21f6b66ea646c6e24e5801023557e8b5db3831d6.camel@paulk.fr>
Date:   Tue, 09 Oct 2018 19:48:09 +0200
From:   Paul Kocialkowski <contact@...lk.fr>
To:     Tomasz Figa <tfiga@...omium.org>
Cc:     Alexandre Courbot <acourbot@...omium.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Hans Verkuil <hverkuil@...all.nl>,
        Pawel Osciak <posciak@...omium.org>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v2] media: docs-rst: Document m2m stateless video
 decoder interface

Hi,

Le mardi 09 octobre 2018 à 16:30 +0900, Tomasz Figa a écrit :
> On Thu, Oct 4, 2018 at 9:46 PM Paul Kocialkowski <contact@...lk.fr> wrote:
> > 
> > Hi,
> > 
> > Here are a few minor suggestion about H.264 controls.
> > 
> > Le jeudi 04 octobre 2018 à 17:11 +0900, Alexandre Courbot a écrit :
> > > diff --git a/Documentation/media/uapi/v4l/extended-controls.rst b/Documentation/media/uapi/v4l/extended-controls.rst
> > > index a9252225b63e..9d06d853d4ff 100644
> > > --- a/Documentation/media/uapi/v4l/extended-controls.rst
> > > +++ b/Documentation/media/uapi/v4l/extended-controls.rst
> > > @@ -810,6 +810,31 @@ enum v4l2_mpeg_video_bitrate_mode -
> > >      otherwise the decoder expects a single frame in per buffer.
> > >      Applicable to the decoder, all codecs.
> > > 
> > > +.. _v4l2-mpeg-h264:
> > > +
> > > +``V4L2_CID_MPEG_VIDEO_H264_SPS``
> > > +    Instance of struct v4l2_ctrl_h264_sps, containing the SPS of to use with
> > > +    the next queued frame. Applicable to the H.264 stateless decoder.
> > > +
> > > +``V4L2_CID_MPEG_VIDEO_H264_PPS``
> > > +    Instance of struct v4l2_ctrl_h264_pps, containing the PPS of to use with
> > > +    the next queued frame. Applicable to the H.264 stateless decoder.
> > > +
> > > +``V4L2_CID_MPEG_VIDEO_H264_SCALING_MATRIX``
> > 
> > For consistency with MPEG-2 and upcoming JPEG, I think we should call
> > this "H264_QUANTIZATION".
> 
> I'd rather stay consistent with H.264 specification, which uses the
> wording as defined in Alex's patch. Otherwise it would be difficult to
> correlate between the controls and the specification, which is
> something that the userspace developer would definitely need to
> understand how to properly parse the stream and obtain the decoding
> parameters.

Okay, I agree this makes more sense than trying to keep the names
consistent across codecs.

> > 
> > > +    Instance of struct v4l2_ctrl_h264_scaling_matrix, containing the scaling
> > > +    matrix to use when decoding the next queued frame. Applicable to the H.264
> > > +    stateless decoder.
> > > +
> > > +``V4L2_CID_MPEG_VIDEO_H264_SLICE_PARAM``
> > 
> > Ditto with "H264_SLICE_PARAMS".
> > 
> 
> It doesn't seem to be related to the spec in this case and "params"
> sounds better indeed.

Cheers,

Paul

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