linux-kernel - Re: H264 headers generation for driver

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Message-ID: <561B81B4.1050305@xs4all.nl>
Date:	Mon, 12 Oct 2015 11:47:32 +0200
From:	Hans Verkuil <hverkuil@...all.nl>
To:	Andrey Utkin <andrey.utkin@...p.bluecherry.net>,
	"kernel-mentors@...enic.com" <kernel-mentors@...enic.com>,
	Linux Media <linux-media@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	m.chehab@...sung.com, khalasa <khalasa@...p.pl>
Subject: Re: H264 headers generation for driver

On 09/29/2015 08:59 PM, Andrey Utkin wrote:
> This is a new chapter of tw5864 video grabber & encoder driver
> development drama.
> Last state of code is here (tw5864 branch, drivers/staging/media/tw5864):
> https://github.com/bluecherrydvr/linux/tree/tw5864/drivers/staging/media/tw5864
> 
> Currently I use a third-side LGPL library for H.264 headers generation
> - SPS, PPS and slice headers (because device doesn't generate them).
> It is included as a git submodule "h264bitstream". It is used from
> tw5864-h264.c .
> Of course we want our driver to get to upstream repository when it
> matures enough, that's why we want to ask for advice regarding this.
> I see that there is no similar case in upstream kernel repo - no
> submodules and no libraries for H264 bitstreams.
> Device datasheet
> (http://lizard.bluecherry.net/~autkin/tw5864/tw5864b1-ds.pdf , page
> 47) shows that there's almost no variety of modes, so minimally an
> implementation of bitstream writing functions ue() and se() will
> suffice.
> I guess that one acceptable way is to pre-generate all headers for all
> needed cases and ship them inlined; for correctness checking purpose,
> it is possible to ship also a script or additional source code file
> which is able to generate same headers.
> Please advise.
> 
> Thanks in advance for any kind reply.
> 

You can do something like this:

drivers/media/platform/vivid/vivid-tpg-colors.c

Both the generated tables and the code that generates them are in one
file.

An alternative is to add a source to v4l2-core that generates the tables,
but I don't know if that is feasible (i.e., if it can be made sufficiently
generic).

Regards,

	Hans
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