Re: [PATCH v5 2/4] staging: media: Introduce NVIDIA Tegra video decoder driver

From: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
To: Dmitry Osipenko <digetx@gmail.com>
Cc: Thierry Reding <thierry.reding@gmail.com>,
	Jonathan Hunter <jonathanh@nvidia.com>,
	Stephen Warren <swarren@wwwdotorg.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Mauro Carvalho Chehab <mchehab@kernel.org>,
	Hans Verkuil <hverkuil@xs4all.nl>,
	Vladimir Zapolskiy <vz@mleia.com>,
	Rob Herring <robh+dt@kernel.org>,
	Dan Carpenter <dan.carpenter@oracle.com>,
	linux-media <linux-media@vger.kernel.org>,
	devel@driverdev.osuosl.org,
	devicetree <devicetree@vger.kernel.org>,
	linux-tegra@vger.kernel.org,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Nicolas Dufresne <nicolas.dufresne@collabora.com>
Subject: Re: [PATCH v5 2/4] staging: media: Introduce NVIDIA Tegra video decoder driver
Date: Mon, 23 Nov 2020 00:07:57 -0300	[thread overview]
Message-ID: <CAAEAJfAdGeFK7DNY3QzRZEsZx+PGbQtxyyOPwawmMsx2JByt8g@mail.gmail.com> (raw)
In-Reply-To: <5665b221-04d7-6be9-2377-8006b9563d4b@gmail.com>

On Sat, 21 Nov 2020 at 23:01, Dmitry Osipenko <digetx@gmail.com> wrote:
>
> 22.11.2020 04:02, Ezequiel Garcia пишет:
> > Hi Dmitry,
> >
> ...
> >> +++ b/drivers/staging/media/tegra-vde/TODO
> >> @@ -0,0 +1,4 @@
> >> +TODO:
> >> +       - Implement V4L2 API once it gains support for stateless decoders.
> >> +
> >> +Contact: Dmitry Osipenko <digetx@gmail.com>
> >
> > The API for H264 stateless decoding is ready.
> > See https://lkml.org/lkml/2020/11/18/795.
>
> Hello Ezequiel,
>
> Thank you for the notification! My last attempt at implementing V4L API
> support was about a year ago and it stopped once I realized that there
> is no userspace which uses that API. FFMPEG and chromium browser had
> some kind of V4L support, but it all was oriented at downstream driver
> stacks, and thus, not usable. Do you know what is the current status?
>

The bulk of the API, which relies on the stateless decoder interface [1],
and H264 stateless V4L2 controls has been ready for some time now,
and there are various implementations supporting it.

Chromium supports it [2], and I've tested it on chromebooks,
through chromeos builds. We haven't tried a non-chromeos build,
and I would say it's quite some work.

GStreamer support is available as well. See [3] which should
work for the latest H264 controls (the ones being moved out of staging).

LibreELEC developers maintain an Ffmpeg branch [4], I expect it will
be updated for the latest H264 controls soon, and hopefully merged
in mainline Ffmpeg.

GStreamer and Ffmpeg are relatively straightforward to build and test.

Thanks,
Ezequiel

[1] https://www.kernel.org/doc/html/latest/userspace-api/media/v4l/dev-stateless-decoder.html
[2] https://github.com/chromium/chromium/tree/master/media/gpu/v4l2
[3] https://gitlab.freedesktop.org/ezequielgarcia/gst-plugins-bad/-/tree/h264_stable_uapi
[4] https://github.com/Kwiboo/FFmpeg/tree/v4l2-request-hwaccel-4.3.

> > One minor comment below.
> >
> ...
> >> +       // PPS
> >> +       __u8  pic_init_qp;
> >> +       __u8  deblocking_filter_control_present_flag;
> >> +       __u8  constrained_intra_pred_flag;
> >> +       __u8  chroma_qp_index_offset;
> >> +       __u8  pic_order_present_flag;
> >> +
> >
> > This seems to be bottom_field_pic_order_in_frame_present_flag,
> > as there is no "pic_order_present_flag" syntax element.
>
> Correct, looks like I borrowed that name from the libvdpau API.
>
> https://vdpau.pages.freedesktop.org/libvdpau/struct_vdp_picture_info_h264.html#a405f7ef26ea76bb2c446e151062fc001