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I'm trying to decode a SIP call like below but I don't know anything about this codec. Please help me or suggest me some documents that I should read.

m=audio 49198 RTP/AVP 118
a=rtpmap:118 SIRENLPR/48000/1
a=fmtp:118 bitrate=64000
...
m=video 49200 RTP/AVP 116
b=TIAS:512000
a=content:main
a=label:1
a=rtpmap:116 vnd.polycom.lpr/9000
a=fmtp:116 V=1;minPP=0;PP=150;RS=52;RP=10;PS=1400
...
Frank Shearar
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Ten Ho
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1 Answers1

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It's a proprietary Polycom format. Some of the Siren codecs have been standardised as ITU formats (G.722.1 implements part of Siren 7, for instance G.722.1C implements part of Siren 14 and G.719 is based on Siren 22). LPR is "lost packet recovery", a method Polycom uses to adjust the amount of Forward Error Correction to compensate for high packet loss.

In particular, I think it's a Siren 22 (so G.719) stream, because it's using 48 kHz sampling and a 64kbit bitrate.

Frank Shearar
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