Re: 20bit PCM in 32 bit container

[Giuliano Pochini <pochini@shiny.it>]

On Sun, 4 Mar 2007 01:35:28 +0200
"Maen Suleiman" <maen.suleiman@gmail.com> wrote:

> Hi ,
> 
>  My hardware uses a 20bit PCM format packed in 32bit, ,  I am using a
> 2.6.12 kernel and such a format doesn't exist, is the following enough
> for defining this format:
> 
>  1) defning a new value in 'enum sndrv_pcm_format'
>  2) adding new entry to pcm_formats[SNDRV_PCM_FORMAT_LAST+1] array
> that describes the new format .
> 
> 	[SNDRV_PCM_FORMAT_S20_NEW_LE] = {
> 		.width = 20, .phys = 32, .le = 1, .signd = 1,
> 		.silence = {},
> 	},

I suggest SND_PCM_FORMAT_S20_LE (ie. 20 bits signed data right-aligned in 32
bits frame). I never had a serious look at that code, but you at least also
have to add a lot of conversion functions to/from S20_LE in
alsa-lib/src/pcm/plugin_ops.h (look for #ifdef CONV_LABELS) which are used
by alsa-lib/src/pcm/pcm_linear.c:snd_pcm_linear_convert() and by many other
plugins.


--
Giuliano.

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