Dtmf codec rates when transcoding

[Sergey Zyrianov]

Hello,

I got a question on DTMF rates when transcoding.

A supports AMR/AMR-WB and DTMF with rates 8000 and 16000

B supports only PCMA and DTMF rate of 8000

1. AMR-WB is selected towards A to transcode from PCMA

2. DTMF from B is passed through without jumping to 16000

if this is A's SDP:

m=audio 50010 RTP/AVP 99 97 105 96 a=rtpmap:99 AMR-WB/16000/1 a=fmtp:99 mode-change-capability=2;max-red=0 a=rtpmap:97 AMR/8000/1 a=fmtp:97 mode-change-capability=2;max-red=0 a=rtpmap:105 telephone-event/16000 a=fmtp:105 0-15 a=rtpmap:96 telephone-event/8000 a=fmtp:96 0-15
B's answer looped via rtpengine includes 2 DTMF PTs
m=audio 39682 RTP/AVP 99 96 105

Rtpengine transcodes PCMA to 99 but allows pass through of 96(rate 8000Hz) which makes troubles for A to insert tones into the stream with different rate.

Is this expected behaviour from Rtpengine point of view ?

BR, Sergey

[Richard Fuchs]

Really depends on which version you're running and what the exact signalling looks like. There have been numerous changes and improvements made regarding DTMF over the years.

Cheers

[Sergey Zyrianov]

lets say head of master or latest release - what would be expect behaviour ?

BR, Sergey 

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[Richard Fuchs]

On 13/10/2023 06.46, [EXT] 'Sergey Zyrianov' via rtpengine wrote:
> lets say head of master or latest release - what would be expect
> behaviour ?

Latest version should produce DTMF payload types matching the audio
codecs advertised (absent any signalling flags overriding it).

Cheers