linux-kernel - Re: Stateless Encoding uAPI Discussion and Proposal

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Date:   Wed, 30 Aug 2023 11:18:52 -0400
From:   Nicolas Dufresne <nicolas.dufresne@...labora.com>
To:     Hsia-Jun Li <Randy.Li@...aptics.com>,
        Paul Kocialkowski <paul.kocialkowski@...tlin.com>
Cc:     linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
        Hans Verkuil <hverkuil@...all.nl>,
        Sakari Ailus <sakari.ailus@....fi>,
        Andrzej Pietrasiewicz <andrzej.p@...labora.com>,
        Michael Tretter <m.tretter@...gutronix.de>,
        Jernej Škrabec <jernej.skrabec@...il.com>,
        Chen-Yu Tsai <wens@...e.org>,
        Samuel Holland <samuel@...lland.org>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: Stateless Encoding uAPI Discussion and Proposal

Le mercredi 23 août 2023 à 11:04 +0800, Hsia-Jun Li a écrit :
> > It was suggested so far to leave h264 slice headers writing to the driver. This
> > is motivated by H264 slice header not being byte aligned in size, so the
> H.264, H.265 has the byte_alignment() in nalu. You don't need skip bits 
> feature which could be found in H1.

As you said so, I rechecked the H.264 grammar.

...
  slice_header( )
  slice_data( )
...

There is lot of variable size items in the slice_header() syntax and no padding
bits. And no padding at the start of any of the slice_data types. So no, the
slice_header() syntax in H.264 is not byte aligned like you are claiming here.
Its important to be super accurate about these things, as it will cause errors
to be made. Please always double check.

Nicolas