Wrong sample rate with record_session

[Alienmaster]

Describe the bug
When using record_session in my dialplan (or with mod_audio_fork its the same) and set the record_sample_rate to 16khz it works perfect with Chrome 89. When using Firefox 86 (bot x64 on Windows 10) the rate doubles to 32khz. When changing the sample rate to 8khz it works fine with Firefox.

Update: After some testing i can narrow the problem down to the opus codec. When i comment out the mod_opus module the audio data from both browser is fine.

To Reproduce

1. add the following lines to the dialplan:

<action application="set" data="RECORD_READ_ONLY=true"/>
   <action application="set" data="record_sample_rate=16000"/>
   <action application="record_session" data="/var/freeswitch/meetings/${strftime(%Y-%m-%d-%H-%M-%S)}_${call_uuid}.wav"/>

2. Join a call with Chrome and record a file. Join a call with Firefox also record a file.
3. Compare the frequency with eg audacity.

Expected behavior
A record with everytime 16khz sample rate

Package version or git hash

• Version 1.10.4 in BigBlueButton

I use FreeSwitch in BigBlueButton 2.2.

[dragos-oancea]

check the SDP . Firefox vs Chrome . The difference may be coming from Opus's fmtp.

[Alienmaster]

After some testing i was able to narrow it down to the opus codec. I check the SDP.

[Alienmaster]

When I compare the two Local SDP messages, I notice the following:
Chrome:

a=rtpmap:110 telephone-event/48000

and Firefox:

a=rtpmap:101 telephone-event/8000

[dragos-oancea]

The telephone-event is unrelated. Maybe it has something to do with Firefox setting "stereo=1" .

[Alienmaster]

Is there a way to force this as "mono"?

[dragos-oancea]

try this patch #1115 . put this in opus cfg: <param name="mono" value="1"/>

[dragos-oancea]

the patch will enforce mono. however, I tried to reproduce what you say about the sample rate with Firefox, but I didn't get the same as you, I get a stereo file at 16 khz with the above settings in dialplan, which is expected.

[Alienmaster]

The whole snippet is this: (due to my fault with the code formatting github didn't show the first line)

<action application="set" data="RECORD_READ_ONLY=true"/>
   <action application="set" data="record_sample_rate=16000"/>
   <action application="record_session" data="/var/freeswitch/meetings/${strftime(%Y-%m-%d-%H-%M-%S)}_${call_uuid}.wav"/>

I made the changes to mod_opus and got the same results: Chrome is fine and Firefox isn't.

Update: On Android 11 its the same with both browsers

[dragos-oancea]

please show FS debug logs (both browsers)

[Alienmaster]

freeswitch.log
The first connection is Firefox the second is Chrome

[dragos-oancea]

Needs fix in core media:

if (!zstr((char *) mmap->rm_fmtp) && switch_stristr("stereo=1", (char *) mmap->rm_fmtp)) {
pmap->channels = 2;
} else {
pmap->channels = 1;
}

[Alienmaster]

I guess you mean this file: https://github.com/signalwire/freeswitch/blob/master/src/switch_core_media.c#L5776
What do i need to change?

[dragos-oancea]

I pushed a commit that does a change in the code I've shown. You will need to add a param to autoload_configs/switch.conf.xml . <param name="max-audio-channels" value="1"/> . Both params (the one in opus cfg too) must be used.

[Alienmaster]

Could you please link me the commit? I didn't find it, sorry.

[dragos-oancea]

This branch with the 2 commits: #1115

[dragos-oancea]

the branch was merged.