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

[Alexander Gordeev <alexander.gordeev@opensynergy.com>]

Hi Alexandre,

On 08.12.22 08:23, Alexandre Courbot wrote:
> Add the specification of the video decoder and encoder devices, which
> can be used to provide host-accelerated video operations to the guest.
>
> Signed-off-by: Keiichi Watanabe <keiichiw@chromium.org>
> Signed-off-by: Alexandre Courbot <acourbot@chromium.org>
> --
> Here is the long-overdue new revision of the virtio-video RFC. This
> version reorganizes the specification quite a bit and tries to simplify
> the protocol further. Nonetheless, it still results in a rather long (17
> pages) specification for just these devices, even though the spec is not
> fully complete (I want to rethink the formats descriptions, and some
> parameters need to be added for the encoder device).
>
> I would like to get some high-level feedback on this version and maybe
> propose to do things a bit differently before people invest too much
> time reviewing this in depth. While rewriting this document, it became
> more and more obvious that this is just a different, and maybe a bit
> simpler, reimplementation of the V4L2 stateless decoder protocol [1]. I
> am now wondering whether it would not make more sense to rewrite this
> specification as just a way to transport V4L2 requests over virtio,
> similarly to how virtio-fs does with the FUSE protocol [2].
>
> At the time we started writing this implementation, the V4L2 protocols
> for decoders and encoders were not set in stone yet, but now that they
> are it might make sense to reconsider. Switching to this solution would
> greatly shorten the virtio-video device spec, and also provide a way to
> support other kind of V4L2 devices like cameras or image processors at
> no extra cost.
>
> Note that doing so would not require that either the host or guest uses
> V4L2 - the virtio video device would just emulate a V4L2 device over
> virtio. A few adaptations would need to be done regarding how memory
> types work, but otherwise I believe most of V4L2 could be used as-is.
>
> Please share your thoughts about this, and I will either explore this
> idea further with a prototype, or keep moving the present spec forward,
> hopefully at a faster pace.
>
> Due to the RFC state of this patch I have refrained from referencing the
> normative statements in conformance.tex - I will do that as a final step
> once the spec is mostly agreed on.
>
> [1] https://ddec1-0-en-ctp.trendmicro.com:443/wis/clicktime/v1/query?url=https%3a%2f%2fdocs.kernel.org%2fuserspace%2dapi%2fmedia%2fv4l%2fdev%2dstateless%2ddecoder.html&umid=8ec8d8c9-b83c-40de-9337-a377056fe2af&auth=53c7c7de28b92dfd96e93d9dd61a23e634d2fbec-e98508782bc1c9aa6b2e4a9df9d4dd170f9a5ffa
> [2] https://github.com/oasis-tcs/virtio-spec/blob/master/virtio-fs.tex
>
> Full PDF:
> https://ddec1-0-en-ctp.trendmicro.com:443/wis/clicktime/v1/query?url=https%3a%2f%2fdrive.google.com%2ffile%2fd%2f1HRVDiDdo50%2dS9X5tWgzmT90FJRHoB1dN%2fview%3fusp%3dsharing&umid=8ec8d8c9-b83c-40de-9337-a377056fe2af&auth=53c7c7de28b92dfd96e93d9dd61a23e634d2fbec-e315af79a067165e908bf1d803441eb181e2f375
>
> PDF of video section only:
> https://ddec1-0-en-ctp.trendmicro.com:443/wis/clicktime/v1/query?url=https%3a%2f%2fdrive.google.com%2ffile%2fd%2f1Sm6LSqvKqQiwYmDE9BXZ0po3XTKnKYlD%2fview%3fusp%3dsharing&umid=8ec8d8c9-b83c-40de-9337-a377056fe2af&auth=53c7c7de28b92dfd96e93d9dd61a23e634d2fbec-b5c45bb4b6ccc5b73ea2a54e26f151d61722d0df

One more thing. I haven't found profiles and levels for the encoder
anywhere in the spec. They were there in v5.

--
Alexander Gordeev
Senior Software Engineer

OpenSynergy GmbH
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