Subject: Re: [linux-audio-dev] a central problem with *any* Port model?
From: Abramo Bagnara (abramo_AT_alsa-project.org)
Date: Thu May 24 2001 - 10:23:22 EEST
Paul Davis wrote:
>
> You might have wondered what the "request_monitor_input" and related
> parts of my proposed API were for.
>
> Input monitoring is a critical part of most audio systems. It is
> accomplished most efficiently by the component closest to the h/w.
> Thus, although in theory you could use a "monitor" plugin that feeds
> its inputs to its outputs (presumably by tieing the two Ports
> together), this is less efficient than doing it in the Driver
> currently being used. This allows the driver to monitor input
> *without* h/w-format-to-s/w-format-to-h/w-format conversions. In the
> "alsadriver" object that I wrote, its accomplished with either memcpy
> or a variant that handles interleaving.
>
> So yes, a plugin could do it, but its less efficient. There is also
> the problem that if its done by a plugin, objects which desire
> input monitoring to be in effect do not know who to ask to make this
> happen. An example is Ardour's Route and DiskStream objects, both of
> which have methods which cause them to want to request that their
> inputs be monitored. In a plugin-based system, how would they know who
> to ask?
>
> But wait a minute! Oh my, this is much worse than I thought. Much
> worse. There isn't *any* way to monitor the input of a Port in
> general! If it happens to be a port on a Driver that is controlling an
> audio h/w interface, then its possible. But in the general case, the
> notion of monitoring a Port is nonsensical - there is no mechanism to
> do it.
>
> Gulp. This seems bad.
>
> How can anyone build a disk recorder that cannot monitor its input
> effectively?
I've not understood what's the problem...
I see you've problems if you limit port data type to float ;-).
Someone can explain which other problems exists?
-- Abramo Bagnara mailto:abramo_AT_alsa-project.orgOpera Unica Phone: +39.546.656023 Via Emilia Interna, 140 48014 Castel Bolognese (RA) - Italy
ALSA project http://www.alsa-project.org It sounds good!
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