Re: Hantro H1 Encoding Upstreaming

[Paul Kocialkowski <paulk@sys-base.io>]

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Hi,

Le Wed 15 Jan 25, 14:51, Nicolas Dufresne a écrit :
> Le mercredi 15 janvier 2025 à 16:03 +0100, Paul Kocialkowski a écrit :
> > We could have some common per-codec bitstream generation v4l2 code with either
> > a cpu buffer access backend or a driver-specific implementation for writing the
> > bits. I already have a base for this in my cedrus h264 encoder work:
> > https://github.com/bootlin/linux/blob/cedrus/h264-encoding/drivers/staging/media/sunxi/cedrus/cedrus_enc_h264.c#L722
> 
> There is a lot of code in there that you can throw directly into v4l2-h264, this
> is exactly what that library is meant for. It had never meant to be limited to
> generating intermediate reference lists for decoders, or to be decoder specific.
> Note that golomb coding can further be generalized.
> 
> I do agree at least for now that letting the driver write headers have more
> advantages. It allows notably to turn off the knobs that would not otherwise be
> supported.

Yes it seems common that hardware will not support certain features or values
and need some bitstream values set to some hard-coded values. There's also
various controls for the stateful API that define most of the basic things that
can be configured in the SPS/PPS. Then each driver exposing what it supports
is a pretty good fit.

> The modification would of course be reference at s_ctrl time,
> assuming you reuse existing sps/pps and other similar compound controls. As we
> didn't have encoder in mind when we created these compound controls, its
> possible that we'll have to add an extended one to fill the gaps, which has
> always been the plan.

I'm not really sure it's needed to pass the whole pps/sps in controls.
Reusing the individual stafeul controls feels like a good fit from what I can
see. And yes we'd need some extra info to be passed from userspace about things
like frame type, qp, etc that will impact the generated bitstream.

Paul

-- 
Paul Kocialkowski,

Independent contractor - sys-base - https://www.sys-base.io/
Free software developer - https://www.paulk.fr/

Expert in multimedia, graphics and embedded hardware support with Linux.

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