嘿,我想知道在WebRTC中创建offer/answer时是否有选择编解码器的方式。目前可供选择的视频编解码器并不多,但有一些音频编解码器,如Opus、PCMU、PCMA等。
嘿,我想知道在WebRTC中创建offer/answer时是否有选择编解码器的方式。目前可供选择的视频编解码器并不多,但有一些音频编解码器,如Opus、PCMU、PCMA等。
一般来说是可以的。以下是如何在建立连接时优先选择Opus编解码器的示例。 您应该从createAnswer或createOffer的回调函数中调用“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;
};
navigator.mediaDevices.getUserMedia({
audio: {
autoGainControl: false,
channelCount: 2,
echoCancellation: false,
latency: 0,
noiseSuppression: false,
sampleRate: 48000,
sampleSize: 16,
volume: 1.0
}
});
然后将SDP设置为 stereo
并增加 maxaveragebitrate
:
let answer = await peer.conn.createAnswer(offerOptions);
answer.sdp = answer.sdp.replace('useinbandfec=1', 'useinbandfec=1; stereo=1; maxaveragebitrate=510000');
await peer.conn.setLocalDescription(answer);
a=fmtp:111 minptime=10;useinbandfec=1; stereo=1; maxaveragebitrate=510000
这意味着立体声的潜在最大比特率为520kb/s,每个通道为260kps。实际比特率取决于您的网络速度和信号强度。
您可以在以下链接中了解更多其他可用属性:https://www.rfc-editor.org/rfc/rfc7587
let tcvr = pc.getTransceivers()[0];
let codecs = RTCRtpReceiver.getCapabilities('audio').codecs;
let opus_codecs = [];
// iterate over supported codecs and pull out the codecs we want
for(let i = 0; i < codecs.length; i++)
{
if(codecs[i].mimeType == "audio/opus")
{
opus_codecs .push(codecs[i]);
}
}
// currently not all browsers support setCodecPreferences
if(tcvr.setCodecPreferences != undefined)
{
tcvr.setCodecPreferences(opus_codecs);
}
从Pericror博客文章改编的代码,用于修复音频/视频编解码器。