Is there a way to select codecs in WebRTC PeerConnection?

Question

Hi, I would like to know if there is a way to select codecs when creating a proposal / response in WebRTC. There are currently not many video codecs to choose from, but there are audio codecs such as Opus, PCMU, PCMA, etc.

Answer 1

In general, yes. Here is an example of how to select the Opus codec during connection setup. You must call 'preferOpus' from the callback function for createAnswer or createOffer.

var preferOpus = function(sdp) { var sdpLines = sdp.split('\r\n'); for (var i = 0; i < sdpLines.length; i++) { if (sdpLines[i].search('m=audio') !== -1) { var mLineIndex = i; break; } } if (mLineIndex === null) return sdp; for (i = 0; i < sdpLines.length; i++) { if (sdpLines[i].search('opus/48000') !== -1) { var opusPayload = extractSdp(sdpLines[i], /:(\d+) opus\/48000/i); if (opusPayload) sdpLines[mLineIndex] = setDefaultCodec(sdpLines[mLineIndex], opusPayload); break; } } sdpLines = removeCN(sdpLines, mLineIndex); sdp = sdpLines.join('\r\n'); return sdp; }; var extractSdp = function(sdpLine, pattern) { var result = sdpLine.match(pattern); return (result && result.length == 2)? result[1]: null; }; var setDefaultCodec = function(mLine, payload) { var elements = mLine.split(' '); var newLine = new Array(); var index = 0; for (var i = 0; i < elements.length; i++) { if (index === 3) newLine[index++] = payload; if (elements[i] !== payload) newLine[index++] = elements[i]; } return newLine.join(' '); }; var removeCN = function(sdpLines, mLineIndex) { var mLineElements = sdpLines[mLineIndex].split(' '); for (var i = sdpLines.length-1; i >= 0; i--) { var payload = extractSdp(sdpLines[i], /a=rtpmap:(\d+) CN\/\d+/i); if (payload) { var cnPos = mLineElements.indexOf(payload); if (cnPos !== -1) mLineElements.splice(cnPos, 1); sdpLines.splice(i, 1); } } sdpLines[mLineIndex] = mLineElements.join(' '); return sdpLines; };