Subject: Re: video4linux user land API concern
From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: Hubert Tonneau <hubert.tonneau@fullpliant.org>
Cc: linux-kernel@vger.kernel.org
In-Reply-To: <05G2L0Z12@briare1.heliogroup.fr>
References: <05G2L0Z12@briare1.heliogroup.fr>
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Date: Wed, 09 Nov 2005 12:31:14 +0000
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On Mer, 2005-11-09 at 10:26 +0000, Hubert Tonneau wrote:
> Any Video4Linux driver should support both native hardware color encoding
> (for maximum performances) and rgb (for maximum flexibility).
> 
> Requiering user land tools to be prepared to match the webcam native color
> encoding is poor kernel API design for several reasons:

The kernel API was designed on the basis that someone would one day have
the sense to write a nice user space library of formats. 

> . if new color models appear in new cameras, the current design will require
>   to map them anyway to some existing encodings not to break existing softwares,
>   so the end result will be even more confusing because the driver supporting a
>   non rgb encoding will not necessary mean that selecting the encoding is better
>   from the performances point of view

Many of the encodings done by hardware are extremely complicated and
tricky to unpack in kernel space. If a camera captures jpeg for example
you don't want in kernel jpeg decoders, let alone mpeg decoders etc

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