有沒有辦法在WebRTC PeerConnection中選擇編解碼器？

Question

嘿，我想知道在WebRTC中創建報價/回答時是否有任何方式選擇編解碼器。目前沒有多少視頻編解碼器可供選擇，但有Opus，PCMU，PCMA等音頻編解碼器。

Answer 1

一般來說，是的。以下是建立連接期間如何選擇Opus編解碼器的示例。 您應該從createAnswer或createOffer的回調函數中調用'preferOpus'。

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; 
};