gstreamer/ext/alsa/README

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0.0 History
-----------
This plugin was originally written by Thomas Nyberg <thomas@codefactory.se> for
ALSA 0.5.x. It was updated and changed quite a bit in September 2001 by Andy
Wingo for use with ALSA 0.9.x. It was rewritten in great part again by Benjamin
Otte in January/February 2003.
1.0 Introduction
----------------
This plugin was designed for use with ALSA 0.9.x, using other versions most
assuredly will not work.
The plugin will probe which cards and pcm-devices that are availible, and then
it tries to determine their capabilities. This will allow the use of multiple
cards with multiple pcm-devices - at the same time! Since I only have one card
on my system, as of yet, I haven't had the chance to try this out.
2.0 How to use it
-----------------
Since we can have multiple soundcards, each having the same name - and also
multiple pcm-devices on each card, a problem with naming occurs. When
the alsa-plugins are initialized, a factory is created for each card and
pcm-device on the system.
On my desktop, I have the following:
wingo@cebreiro:~/src/gstreamer$ gstreamer-inspect alsa
INFO ( 339:-1) Initializing GStreamer Core Library
INFO ( 339:-1) CPU features: (808009bf) MMX 3DNOW
Plugin Details:
Name: alsa
Long Name: Alsa plugin library
Filename: /usr/lib/gst/libalsa.so
ES1370/1_sink: ES1370 DAC2/ADC
ES1370/2_sink: ES1370 DAC1
ES1370/1_src: ES1370 DAC2/ADC
alsasink: default alsa sink
alsasrc: default alsa src
My particular card has 4 channel out and 2 channel in. As you can see, each of
these devices are stereo. The alsasink and alsasrc elements correspond to the
default alsa devices.
3.0 Where to look for other ALSA drivers
----------------------------------------
ALSA 0.9 isn't very well documented, so we had to rely on a number of different
sources for guidance. Sources of inspiration include JACK's alsa driver
(available in jack's cvs tree, http://jack.sourceforge.net/), the alsa2 driver
of mplayer (http://www.mplayerhq.hu) and the pcm.c example from the ALSA library
itself.
(http://www.alsa-project.org/alsa-doc/alsa-lib/_2test_2pcm_8c-example.html)
4.0 License
-----------
This plugin is licensed under the Lesser General Public License (LGPL). See the
file COPYING in the top source directory.