linux-kernel - Re: [PATCH v3 2/2] media: docs-rst: Document memory-to-memory video encoder interface

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Date:   Mon, 15 Apr 2019 08:30:03 -0400
From:   Nicolas Dufresne <nicolas@...fresne.ca>
To:     Tomasz Figa <tfiga@...omium.org>
Cc:     Hans Verkuil <hverkuil@...all.nl>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Pawel Osciak <posciak@...omium.org>,
        Alexandre Courbot <acourbot@...omium.org>,
        Kamil Debski <kamil@...as.org>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Jeongtae Park <jtp.park@...sung.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Tiffany Lin (林慧珊) 
        <tiffany.lin@...iatek.com>,
        Andrew-CT Chen (陳智迪) 
        <andrew-ct.chen@...iatek.com>,
        Stanimir Varbanov <stanimir.varbanov@...aro.org>,
        Todor Tomov <todor.tomov@...aro.org>,
        Paul Kocialkowski <paul.kocialkowski@...tlin.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        dave.stevenson@...pberrypi.org,
        Ezequiel Garcia <ezequiel@...labora.com>,
        Maxime Jourdan <maxi.jourdan@...adoo.fr>
Subject: Re: [PATCH v3 2/2] media: docs-rst: Document memory-to-memory video
 encoder interface

Le lundi 15 avril 2019 à 17:56 +0900, Tomasz Figa a écrit :
> > Sounds like we need something similar to the SOURCE_CHANGE event
> > mechanism if we want to allow dynamic bitrate control which would
> > require re-allocation of the capture buffer queue. (Or any other
> > runtime control on our encoders, which is really expected to be
> > supported these days).
> 
> Sounds like it. Or we could just assume that one needs to stop both
> queues to do a resolution change, since most codes would anyway reset
> the stream (e.g. send PPS/SPS, etc. for H.264) to change the
> resolution. Not sure if that assumption always holds, though.

I think for resolution/profile/level changes you have a good point, as
you said, we need to start a new stream (new header, new IDR). Maybe
then we should simply require the driver to allocate enough buffer to
support the highest bitrate for the selected resoltion/profile/level?
Though, this could create situation where we waste a lot of memory. On
the other side, if you need to reallocate your buffers on bitrate
change, it might create a visible freeze.

Nicolas