[Speex-dev] Enabling Speex VBR for VoIP

Tom Grandgent tgrand at canvaslink.com
Sat Jun 28 08:48:56 PDT 2008

Jean-Marc Valin <jean-marc.valin at usherbrooke.ca> wrote:
> See the SPEEX_SET_VBR and SPEEX_SET_VBR_QUALITY options. But be aware
> that unless you're aggregating many VoIP calls on the same link, there's
> little use for VBR in VoIP.

I don't agree with this.  I've used Speex's VBR mode exclusively in my 
P2P VoIP software for the past 4 years and never had reason to regret 
it.  I use it to achieve a better tradeoff between bandwidth usage and 
quality and to let the user very easily adjust this tradeoff via one 
simple slider.

VBR lets you use less bandwidth than CBR to achieve a certain level of 
quality.  That is its purpose.  Using less bandwidth has plenty of 
advantages in many VoIP scenarios: more bandwidth available for other 
stuff, possibly lower packet loss/latency/jitter, lower costs for 
those who are unfortunate enough to be stuck with metered connections, 
and the perceived advantage of using a lower total amount of bandwidth. 
Also, if everyone gave bandwidth usage a little more consideration in 
designing their systems, we might have better quality of service on 
shared networks.

I understand that CBR is a better choice in some situations.  Sometimes 
it can be useful to control exactly how much bandwidth is used, even if 
that means wasting some of it.  I just think you give VBR too little 


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