[Freeswitch-users] FEC and bitrates

[Dragos Oancea]

David,

Most likely your mod_opus is configured to respect the remote's fmtp and
not the maxaveragebitrate and maxplaybackrate that you configure. You have
bitrate-negotiation set to true.
It looks it's going in WB mode if you are sure it starts sending FEC at
over 16 kbit/s .
Value 14400 was chosen as config default only because is one step above
14000 which is one of the LBRR thresholds (Opus's bitrate works in steps of
400 bits/s) and it also provides a good compromis loss/audio quality for
NB.
https://github.com/xiph/opus/blob/master/silk/define.h#L52

/* LBRR thresholds */
#define LBRR_NB_MIN_RATE_BPS 12000
#define LBRR_MB_MIN_RATE_BPS 14000
#define LBRR_WB_MIN_RATE_BPS 16000


FEC threshold in FS is this:
#define SWITCH_OPUS_MIN_FEC_BITRATE 12400 - one step above codec's LBRR
threshold for NB. LBRR means Low Bit Rate Redundancy which means FEC.

Regards,
Dragos




On Sat, Dec 18, 2021 at 3:06 AM David Villasmil <
david.villasmil.work at gmail.com> wrote:

> Hello all,
>
> i've been testing FEC and how low we can go with maxavgbiterate
>
> <param name="use-vbr" value="1"/>
> <param name="use-dtx" value="1"/>
> <param name="complexity" value="10"/>
> <param name="packet-loss-percent" value="15"/>
> <param name="asymmetric-sample-rates" value="1"/>
> <param name="bitrate-negotiation" value="1"/>
> <param name="keep-fec-enabled" value="1"/>
> <param name="use-jb-lookahead" value="true"/>
> <param name="maxaveragebitrate" value="14400"/>
> <param name="maxplaybackrate" value="8000"/>
> <param name="sprop-maxcapturerate" value="0"/>
> <param name="adjust-bitrate" value="1"/>
>
> we only see FEC if we set maxavgbiterate to 18000, we see no FEC with 14400
>
> anyone knows what i'm missing?
>
> Regards,
>
> David Villasmil
> email: david.villasmil.work at gmail.com
> phone: +34669448337
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