Speex dev - Jan 2009 - Echo cancellation and synchronization

Hi Jean-Marc and all others!

I am having some troubles with the echo cancellation feature of speex in 
a voip project. I have two threads, one for sound input and one for 
sound output.
In the output thread, I call speex_echo_playback(). or every frame sent 
to the sound card. In the input thread, I call speex_echo_capture() for 
every frame captured from the sound card. Also, I do encoding/decoding, 
networking etc.

This all works fine on my MacBook. But when I run the same application 
on a linux machine I continuously receive the following speex warnings:

warning: Had to discard a playback frame (your application is buggy 
and/or got xruns)
warning: Auto-filling the buffer (your application is buggy and/or got 
xruns)
warning: Had to discard a playback frame (your application is buggy 
and/or got xruns)
warning: Auto-filling the buffer (your application is buggy and/or got 
xruns)
...
...

The problem seems to be that the sound output thread (and thus 
speex_echo_playback()) sometimes executes three frames/"iterations" 
before the sound input thread (and thus speex_echo_capture()) comes in. 
How do I deal with this problem? I suspect I cannot really affect how 
often the sound card lib requires a new frame or has one available.

Regards,
Peter

Peter Vestberg a ?crit :
> The problem seems to be that the sound output thread (and thus 
> speex_echo_playback()) sometimes executes three
frames/"iterations"
> before the sound input thread (and thus speex_echo_capture()) comes in. 
> How do I deal with this problem? I suspect I cannot really affect how 
> often the sound card lib requires a new frame or has one available.
Then I suggest doing the buffering yourself and using
speex_echo_cancellation() instead of the playback() and capture() calls.

	Jean-Marc

Thanks for your quick response.

Do you know how many playback frames that would be considered "ok" to
buffer up in this scenario? I've tested the speexclient application and
got similar results. There isn't any option to the
playback/capture-mechanism for adjusting the buffer size? It feels like
doing my own buffering would simply be a copy paste of your buffering
but with a larger buffer size. I am bit confused here :-)

Regards,
Peter

Jean-Marc Valin wrote:
> Then I suggest doing the buffering yourself and using
> speex_echo_cancellation() instead of the playback() and capture() calls.
>
> 	Jean-Marc
>
>