Re: [9fans] audio standards -- too many to choose from

[Bakul Shah <bakul+plan9@bitblocks.com>]

On Sat, 15 Aug 2009 05:24:01 +0800 sqweek <sqweek@gmail.com>  wrote:
> On 12/08/2009, Tim Newsham <newsham@lava.net> wrote:
> > Draw the line at what the hardware can be told to decode
> > with a flip of a register?  The driver interface can easily
> > accomodate arbitrary encoding names (see inferno's driver
> > for an example).
>
>  One thing I haven't seen mentioned (perhaps because I misunderstand)
> is the added state that comes from allowing multiple formats.
> Actually, I think this problem exists with the current interface
> already - say I have a program playing music at 44kHz and then I get
> an email or something that I've set up to cause an aural alert, but
> the program that does that wants to work at 22kHz. This sort of
> interaction sounds bad enough to me, I don't even want to think about
> what it would sound like if the music was in mp3 and the alert changed
> the kernel format to wav.

The mixer would have to be smart.

>  I guess this is where mixerfs and the like enter the picture, but
> I've come to think of the kernel as a hardware multiplexer so I'm
> liking the idea of having the kernel support multiple formats.
>  Then again, I also respect the argument that the kernel is not a
> hardware multiplexer but a hardware abstractor - doesn't matter what's
> down there the kernel provides the same interface. From this point of
> view the simple approach is compelling, have /dev/audio exclusive
> write to avoid the above sort of interaction and mix in userspace (or
> is there still playback/recording sample rate interaction?). I think
> everyone agrees it doesn't make sense to have an mp3 decoder
> in-kernel...
> -sqweek

A decoder is just a resource (like a mouse, keyboard, disk,
network interface etc.).  If h/w provides an mp3 decoder it
would be nice to be able to use it.

One idea is to have a devicename for each format/samplerate.
Some would be backed by h/w, some provided solely by s/w.
Basically you need an ability to interpose some sort of
"stream" module to create a network.