From mboxrd@z Thu Jan  1 00:00:00 1970
Date: Tue, 11 Aug 2009 16:07:54 -1000
From: Tim Newsham <newsham@lava.net>
To: Fans of the OS Plan 9 from Bell Labs <9fans@9fans.net>
In-Reply-To: <38fa4d234fa7ff8613123fe9a6921943@quanstro.net>
Message-ID: <Pine.BSI.4.64.0908111557570.20861@malasada.lava.net>
References: <38fa4d234fa7ff8613123fe9a6921943@quanstro.net>
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Subject: Re: [9fans] audio standards -- too many to choose from
Topicbox-Message-UUID: 42f59d60-ead5-11e9-9d60-3106f5b1d025

> i didn't mean translating from one /dev/audio to the next.
> i ment dealing with azalia audio vs. ac97 vs. soundblaster.
> and ogg/vorbis vs. mp3 vs pem vs. *law.

I agree here.  I envision a separate codec server that
sits on top of an audio server and encapsulates a bunch
of this stuff.  It would be nice if it was practical
to  "cat foo.mp3 >/dev/codec/mp3" or something like that..
I haven't really thought this through much, just daydreaming
this feature...

> i would be interested in a solid implementation.  i haven't
> yet spent any serious time looking at the various ac'97 drivers
> but they didn't seem to me to go quite far enough in defining
> an audio universe.  that's one thing that draw(2) does do
> that i would hope audio would do as well.

I'm not familiar with what ac97 provides.  Can you describe
a little what the features are and what you think an interface
should be like?

Here's a brief rundown of what I was thinking about, somewhat
based on the inferno driver:

    $ cat /dev/audioctl
    enc pcm8 pcm16le pcmu16be ulaw
    rate 44100 8000 11025 22050
    chans 2 1

    meaning that the device is currently in pcm8 at 44.1khz
    and 2 channels (stereo).  (Inferno's driver would have
    said enc "pcm" with bits "8" instead of saying "pcm8",
    but I feel that separating out bits and possibly endian
    for "pcm" adds complication since the encoding "pcm-16-unsigned"
    isnt really a separable thing).

    $ echo "rate 11025" >/dev/audioctl
    $ echo "chans 1" >/dev/audioctl
    $ cat /dev/audioctl
    enc pcm8 pcm16le pcmu16be ulaw
    rate 11025 44100 8000 22050 44100
    chans 1 2
    $ dd if=/dev/audio of=sound bs=4096

    now we have 4k samples of 11khz mono audio in "sound"

additionally it might be useful to support some of the
stat features from usbaudio or plan9 audio(3), such
as the ability to figure out the dma size, how much data
is buffered, and the timing associated with samples being
read.

> - erik

Tim Newsham
http://www.thenewsh.com/~newsham/