有没有办法在WebRTC PeerConnection中选择编解码器？ [英] Is there a way to choose codecs in WebRTC PeerConnection?

问题描述

嘿，我想知道在WebRTC中创建报价/答案时是否可以选择编解码器。当前没有很多视频编解码器可供选择，但是有音频编解码器，如Opus，PCMU，PCMA等。

Hey I would like to know if there is any way to choose codecs when creating the offer/answer in WebRTC. There are currently not many video codecs to choose from, but there are audio codecs like Opus, PCMU, PCMA etc.

推荐答案

在一般，是的。这是在建立连接时如何首选Opus编解码器的示例。
您应该从回调函数中为createAnswer或createOffer调用 preferOpus。

In general, yes. Here is example of how to prefer Opus codec during establishing conneciton. You should call 'preferOpus' from a 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;
};

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