Are multiple codecs being used during an ongoing call?

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Abhinav Ananth

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Aug 9, 2023, 4:30:43 AM8/9/23
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Hello,

So I was under the impression that multiple codecs might be send and received in the SDP but once it is set to the stack (setRemoteDescription, selLocalDescription), only one of them would be used for audio and one for video. But checking the output of the following code shows mulitple codecs - 

peerConnection.getSenders()[0].getParameters().codecs ->.
[
{
"channels": 2,
"clockRate": 48000,
"mimeType": "audio/opus",
"payloadType": 111,
"sdpFmtpLine": "maxaveragebitrate=32000;maxptime=20;minptime=10;ptime=20;stereo=0;useinbandfec=1"
},
{
"channels": 1,
"clockRate": 16000,
"mimeType": "audio/AMR-WB",
"payloadType": 102,
"sdpFmtpLine": "maxptime=20;mode-change-capability=2;octet-align=0;ptime=20"
},
{
"channels": 1,
"clockRate": 8000,
"mimeType": "audio/AMR",
"payloadType": 100,
"sdpFmtpLine": "max-red=0;maxptime=20;mode-change-capability=2;mode-set=0,2,4,7;ptime=20"
},
{
"channels": 1,
"clockRate": 48000,
"mimeType": "audio/telephone-event",
"payloadType": 110,
"sdpFmtpLine": "maxptime=20;ptime=20"
},
{
"channels": 1,
"clockRate": 8000,
"mimeType": "audio/AMR",
"payloadType": 97,
"sdpFmtpLine": "maxptime=20;ptime=20"
}
]

peerConnection.getSenders()[1].getParameters().codecs ->
[
{
"clockRate": 90000,
"mimeType": "video/VP8",
"payloadType": 96
},
{
"clockRate": 90000,
"mimeType": "video/H264",
"payloadType": 127,
"sdpFmtpLine": "level-asymmetry-allowed=1;packetization-mode=1;profile-level-id=42C01F"
}
]

peerConnection.getReceivers()[0].getParameters().codecs ->
[
{
"channels": 2,
"clockRate": 48000,
"mimeType": "audio/opus",
"payloadType": 111,
"sdpFmtpLine": "minptime=10;useinbandfec=1"
},
{
"channels": 1,
"clockRate": 48000,
"mimeType": "audio/telephone-event",
"payloadType": 110
}
]

peerConnection.getReceivers()[1].getParameters().codecs ->
[
{
"clockRate": 90000,
"mimeType": "video/VP8",
"payloadType": 96
}
]


Thanks in advance
R

Philipp Hancke

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Aug 10, 2023, 5:42:39 AM8/10/23
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These are the codecs that are negotiated. Only one of them can be used at a time so .encodings will be an array with a length of 1.

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Abhinav Ananth

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Aug 10, 2023, 5:49:32 AM8/10/23
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Oh I see, so even this shows the list of codecs negotiated? How can I know which codec is currently in use?

Regards

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Philipp Hancke

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Aug 11, 2023, 2:04:59 AM8/11/23
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