linux-kernel - Re: [PATCH v1 2/2] media: staging: tegra-vde: Support V4L stateless video decoder API

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Date:   Tue, 18 Jan 2022 13:43:35 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Nicolas Dufresne <nicolas@...fresne.ca>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Hans Verkuil <hverkuil@...all.nl>
Cc:     linux-media@...r.kernel.org, linux-staging@...ts.linux.dev,
        linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 2/2] media: staging: tegra-vde: Support V4L stateless
 video decoder API

18.01.2022 05:43, Nicolas Dufresne пишет:
> Le mercredi 12 janvier 2022 à 22:04 +0300, Dmitry Osipenko a écrit :
>>> If so, I may suggest to drop this fallback, and propose an amendment to the
>>> spec, we can require flagging KEYFRAME/PFRAME/BFRAME on the OUTPUT buffer,
>>> this
>>> won't break any drivers/userland on other HW, and will benefit possibly
>>> other HW
>>> in the future. I can volunteer to patch GStreamer and LibreELEC ffmpeg if we
>>> agree to this. Not sure how it works for Chromium, or if it actually make
>>> sense
>>> to support here.
>>>
>>> (expecting feedback from Hans and Ezequiel here)
>>
>> Amending the spec will be great, although it's not clear how to flag
>> frame that consists of slices having different types.
> 
> As per spec, all slices of a frame must be of the same type. In short, there is
> no problem, adding new flags to the decode_params.flags is fine, and is backward
> compatible. I had a second thought that I'd probably prefer this over using the
> v4l2_buffer flags, but either way seems backward compatible.
> 
> In H264, but also other CODEC, slices are have two types of parameters, some of
> the parameters are invariant between slices, but still duplicated so you can
> decode some of the frame, even if the very first slice is lost. We tried our
> best to place all the slice invariant parameters in decode_params to keep the
> slice_params as small as we could.

Could you please give a direct reference to the spec? (chapter / page or
provide quote)

I'm vaguely recalling that x264 encoder was able to generate such frames.