[alsa-devel] Full duplex ALSA-plugin

Jaroslav Kysela perex at perex.cz
Tue Jul 10 16:39:16 CEST 2012

Date 10.7.2012 16:28, Christian Gruber wrote:
> I was looking for information on writing an echo cancellation ALSA-plugin. So I studied 
> the ALSA-plugin docs and also found several interesting threads in this mailing list. But 
> what I found out, was quiet disillusioning.
> If I understood the ALSA-plugin concept right, there is no possibility to write a plugin 
> working on two streams, a playback and a record stream, simultaneously. One can only write 
> a filter plugin, which works either on a playback stream or a record stream but not both. 
> And there is no possibility to open a full duplex stream (consisting of playback and 
> record) with snd_pcm_open().
> Is there a reason, why full duplex streams are not implemented yet? Or is it planned in 
> the future to implement this feature?

If you want to do some synchronization between two streams, you have to
use own "data sharing" mechanism such as IPC or so..

In other words - implement filters on both playback and capture streams
and implement the required communication between them.


Jaroslav Kysela <perex at perex.cz>
Linux Kernel Sound Maintainer
ALSA Project; Red Hat, Inc.

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