Subject: Re: [linux-audio-dev] Audio routing issues for linux..
From: Juan Linietsky (coding_AT_reduz.com.ar)
Date: Tue Jun 11 2002 - 00:09:01 EEST
On Mon, 10 Jun 2002 22:49:01 +0200
Vincent Touquet <vincent.touquet_AT_pandora.be> wrote:
> (cut)
> >I'm afraid i didnt make myself clear. I tried to expain this in
> >previous mails, but I think i'm failing so far.
> >I perfectly understand what JACK is, but as I said before,
> >it's primarily meant for low latency stuff.
> >So my proposal consisted in two things.
>
> >1-The first one is to proovide transparent audio routing using
> >_existing apis_, this does work since most apps do proovide
> >standard buffersizes (100/200) ms latency. (As fun as this sounds,
> >many VST/DXi plugins work at these rates using the "windows kernel
> >streaming" hehe :).
> How would you provide an existing API ?!
> So, you have this existing API, and then ?
> You go and change the internals ??
> Do you want to change the semantics of an existing API
> or what ? What do you do with existing code that
> uses this API and relies on its semantics ?
>
I think Kai Vehmanen did a much better job explaining this than
myself, since I dont know the internals of alsalib. I'll just repost
what he said:
-----------------
If we don't worry about low-latency too much, then the situation
changes.
It shouldn't be too big of a task to write an ALSA PCM plugin that
interfaces with jackd using libjack. This would allow all ALSA and OSS
apps to interact with JACK. I'm certain someone will write this bridge
sooner or later. A simplified version would do:
- lock the ALSA hw parameter space to the values given by jackd
- treat JACK like a soundcard
- pcm plugin layer is used to convert between formats used
by JACK and ALSA (here JACK is the 'hw' device)
- when JACK delivers an interrupt, the bridge code
updates the "hwptr" and checks whether ALSA app should be
woken up
- sw-params like avail_min, and start/stop threshold can
be used to control to bridge operation
- ... you get the picture
-------------
Juan Linietsky
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