[asterisk-dev] Support for amr codec?

Michael Maier m1278468 at mailbox.org
Thu Aug 20 13:54:48 CDT 2020

On 20.08.20 at 15:12 Alexander Traud wrote:
>> comfort noise, which is not supported by Asterisk
> In case of AMR(-WB), Comfort Noise (CN) is part of the decoder itself already. Consequently, no additional support in Asterisk is required. My patch can be changed to enable Voice Activity Detection (VAD) in the encoder.

I can hear the distortions on the other side (on the G711 side), therefore I think it's a problem of the decoder during 
transcoding amr -> g711.


>> few small changes to get the patches applied
> Same here. If you have an issue, report it.

That wasn't a problem of the code by itself. The patch just has to be adjusted to Asterisk 16.x additional code lines - 
no trouble at all.

>> Is there a must have to support amr (with Deutsche Telekom)?
> Deutsche Telekom does the transcoding for you. Chapter in
> <https://www.telekom.de/hilfe/downloads/1tr114.pdf>

There are people out there, fearing that Deutsche Telekom could just drop the transcoding w/o any regard to their own 
defined interfaces. Therefore I tested your patches from idle curiosity.

>> any problems with the use of amr and asterisk
> AMR, AMR-WB and 3GPP-EVS are yet another example to unveil the limitations of the SDP media negotiations in Asterisk. This is discussed in GitHub issue #10 and at the remainder of issue #8. I have yet to understand issue #5 in 3GPP-EVS whether the bug is mine. Anyway, I am happy that I reached that far as I had to patch a lot within Asterisk already. But it looks like it is time to leave.

I think it wouldn't be a good idea to leave. Asterisk 18 most probably will have an exciting big change in handling of 
SDP negotiations. One goal is to reduce unnecessary transcodings. But only for pjsip.
See the subjects "Asterisk 18 Planning: Codec Negotiation" and subjects containing "Advanced Codec Negotiation" here in 
the mailing list.

Here you can find some initial documentation [1]


[1] https://wiki.asterisk.org/wiki/display/AST/Codec+Negotiation

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