[Freeswitch-users] OPUS at 48 khz vs OPUS at 8 khz

[doancea]

Hi All,

We've noticed a high load on our transcoding servers when doing
OPUS<->PCMA transcoding.
All our client software is using opus at 48khz, but inside the audio 
payload
we have narrowband audio (forced with  
OPUS_SET_BANDWIDTH(OPUS_BANDWIDTH_NARROWBAND) ) .
Questions :

1.
How can we avoid resampling ?
We've noticed this log line showing twice for each call:
29128b92-d842-11e4-877f-9bd23fac7445 2015-04-01 07:39:14.798759 [NOTICE] 
switch_core_io.c:1287 Activating write resampler

If we modify the client software to use opus at 8khz and leave freeswitch 
as it we have very bad audio (nothing intelligible).

But If we modify the client software to use opus at 8khz and change 
mod_opus.c in freeswitch so it would use only OPUS at 8khz then we have 
proper audio.

2.
We have noticed that there is a "samplerate" param in fmtp (which is not 
in this RFC: 
https://tools.ietf.org/html/draft-spittka-payload-rtp-opus-03 ) it's 
used only for configuring the decoder.
Why only for the decoder ?

If "samplerate" is set then it's passed to opus_encoder_create() , but 
not to opus_decoder_create().


3.
How about using sprop-maxcapturerate to set the sample rate of the 
decoder ?



Regards,
Dragos Oancea