Re: [RFC PATCH v6] virtio-video: Add virtio video device specification

[Alexandre Courbot <acourbot@chromium.org>]

Hi Alexander,

On Thu, Jan 12, 2023 at 2:04 AM Alexander Gordeev
<alexander.gordeev@opensynergy.com> wrote:
> > +\subsubsection{Bitstream formats}\label{sec:Device Types / Video Device / Supported formats / Bitstream formats}
> > +
> > +The fourcc code of each supported bitstream format is given, as well as
> > +the unit of data requested in each input resource for the decoder, or
> > +produced in each output resource for the encoder.
> > +
> > +\begin{description}
> > +\item[\field{MPG2}]
> > +MPEG2 encoded stream. One Access Unit per resource.
> > +\item[\field{H264}]
> > +H.264 encoded stream. One NAL unit per resource.
> > +\item[\field{HEVC}]
> > +HEVC encoded stream. One NAL unit per resource.
> > +\item[\field{VP80}]
> > +VP8 encoded stream. One frame per resource.
> > +\item[\field{VP90}]
> > +VP9 encoded stream. One frame per resource.
> > +\end{description}
> > +
>
> Actually I'm not sure where do these fourcc codes for bitstream formats
> come from.
>
> In one of the old comments I found a reference to
> https://www.rfc-editor.org/rfc/rfc2361
>
> But it doesn't define MPG2, HEVC, VP80, VP90.
>
> Also there is this comment to virtio-video v1 from Tomasz Figa and the
> related discussion:
> https://markmail.org/message/gc6h25acct22niut#query:+page:1+mid:et4l3ni7qjqhiygo+state:results
>
> He wrote that it is not worth it because there are so many conflicting
> sets of fourcc codes.
>
> I can see that fourcc codes were not used in virtio-video spec draft
> versions 1 to 5. So now it looks quite weird to see them here. Probably
> this is because you'd like to mimic v4l2 interface more closely?

These come from here:
https://docs.kernel.org/userspace-api/media/v4l/pixfmt-compressed.html

V4L2 has a nice list of supported fourccs for coded formats, so I'd
just suggest we refer to them and use them instead of defining our
own.