[AG-TECH]too much Bitrate in RAT

[Colin Perkins]

On 21 Jul 2006, at 09:52, John Hodrien wrote:
> On Thu, 20 Jul 2006, Colin Perkins wrote:
>> The way rat works, you always get that delay, no matter what codec  
>> is selected.
>
> Oh.  The optimist in me has gone under his rock.

Rat has a number of settings which change the trade-off between delay  
and quality, if you want to experiment:

1) In the Transmission category of preferences, the "Units" parameter  
determines how many codec frames are included in each packet. Setting  
this to a small values lowers the delay and increases loss  
resilience, at the expense of slightly more bandwidth overhead due to  
the extra RTP headers.

2) In the Transmission category of preferences, enabling redundancy  
increases resilience to loss, at the expense of increased delay. The  
"Offset in Pkts" field determines how many extra packets worth of  
delay is added when enabled.

3) In the Reception category of preferences, you can use the "Limit  
Playout Delay" option to disable the adaptive jitter buffer, and  
manually increase or decrease the playout delay. Use of this is  
usually sub-optimal, since the adaptive buffer works well, but you  
might be able to reduce the latency at the expense of reduced quality  
(enforcing a maximum delay may cause late packets to be discarded,  
instead of played).

4) In the Audio category, increasing the sample rate will reduce the  
delay and increase the quality, at the expense of significant extra  
bandwidth.

5) In the Audio category, enabling "Silence Suppression" (either  
using the automatic setting, or with appropriate manual tuning) will  
reduce the delay compared to Off. This is usually the most  
significant factor in the delay: if you turn silence suppression off,  
delay can build up uncontrollably, since rat has no way to compensate  
for clock skew between sender and receiver sound cards.

You can get statistics on the actual playout delay and network round- 
trip time from the window which opens when you click on a  
participant's name.

Colin